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Windows 11 Boot Loops: How KB5074105 Fixes Startup Errors

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Windows 11 Boot Loops: How KB5074105 Fixes Startup Errors

TechFixBK
||21 min read

Facing Windows 11 boot loops? Discover how the KB5074105 update is designed to resolve startup failures and sign-in errors on versions 24H2 and 25H2.

Address Windows 11 startup failures, authentication errors, and activation bugs using the KB5074105 preview update for versions 24H2 and 25H2.

Hook & Who This Is For

Imagine starting your PC only to find it stuck in a repetitive startup cycle or a frozen sign-in screen. For many users, recent security updates have led to persistent boot loops and system instability that prevent access to the desktop [15][58]. If your device is currently failing to start after a routine update, these reports suggest you are facing a known issue currently being addressed by technical patches [1][59].

Who This Is For

This guide is specifically intended for users and system administrators managing Windows 11 versions 24H2 and 25H2 [21][44]. These specific operating system versions have been identified as the primary targets of the boot failures tied to the January 2026 security updates [51][58].

This article covers:

  • The role of the KB5074105 update in resolving startup and boot-related cycles [3][4].
  • Fixes for sign-in failures and authentication service errors [10][12].
  • Addressing system activation issues triggered by recent update packages [5][14].
  • Confirmation of the specific Windows versions currently susceptible to these errors [8][24].

Note: This overview focuses on software-related boot issues caused by specific Windows updates and may not apply to hardware-driven startup failures.

TL;DR / What This Means for You

The KB5074105 update is an official Windows 11 release designed to improve core system stability [4][5]. It is categorized as an optional preview update, which allows for evaluation before a broader mandatory rollout [14]. This build includes 32 changes and improvements primarily focused on resolving critical startup and authentication errors [15].

Key Insights

  • Resolution for Boot Failures: The update addresses persistent boot loops and startup failures that have previously prevented users from accessing the operating system [1][2][60].
  • Authentication Fixes: Sign-in failures and rejected credential errors within the Windows 11 environment are mitigated by this patch [7][8][11].
  • Activation Repairs: This build resolves issues where the system failed to verify its activation status, including failures in license migration related to online entitlement servers [3][6][12].
  • Technical Refinements: Corrections target core system hangs and licensing malfunctions to ensure consistent OS performance [1][9][30].
  • Manual Installation: If you are experiencing persistent boot cycles or licensing errors, you may manually check for this optional update in Windows Settings [5][10].
  • Pre-Deployment Testing: Because this is a preview build, it is generally recommended to test the update on non-critical systems first, as some reports indicate potential webcam issues [14].
  • Verify Licensing: After installation, users should confirm their activation status to ensure the CLIP / online entitlement migration has completed successfully [12].

While this update stabilizes many high-impact system functions, users should be aware that optional preview releases may introduce minor bugs, such as reported issues with camera functionality in certain configurations [14].

Background / Basics

The KB5074105 update is an optional, non-security preview release for Windows 11 [4][9][13]. Microsoft initiated the rollout in late January 2026, with the update reaching the Release Preview Channel on January 27 [1]. Broader distribution followed on January 29 and January 30, 2026, allowing users to manually install the package to address specific system behaviors [5][7][15].

This update specifically targets two major versions of the operating system: Windows 11 24H2 and Windows 11 25H2 [1][4][11]. According to official documentation, installing this update brings the system build numbers to the following versions:

Windows 11 Version Resulting Build Number
Version 24H2 26100.7705 [10]
Version 25H2 26200.7705 [10]

As a preview release, KB5074105 serves as a technical precursor to the mandatory cumulative updates typically released during the February 2026 Patch Tuesday cycle [13]. It is primarily designed to resolve core system issues, including stability problems related to boot sequences, user sign-in processes, and OS activation [2][3][12].

Microsoft's current reliability efforts focus on these specific builds to ensure that the foundational elements of the 24H2 and 25H2 architectures remain functional for a broad range of hardware [1][4]. In addition to critical fixes, the update potentially introduces minor enhancements to the Settings app and addresses various File Explorer issues [5][11].

Problem Explanation

Recent Windows 11 updates have caused significant disruptions for many users [1][5]. Reports indicate that system stability was compromised following a bug in the January 2026 update [14], leading to widespread frustration and lost productivity as machines became unresponsive [47].

One of the most severe symptoms involves startup failures where devices become stuck in boot loops or display a black screen [5][6]. Technical reports confirm that some affected PCs show the UNMOUNTABLE_BOOT_VOLUME stop code [12][14]. This Black Screen of Death (BSOD) typically requires manual recovery steps to restore functionality [22][47].

Evidence suggests that hardware configuration may play a role in these failures. Specifically, users with Nvidia GPUs have reported experiencing these black screen issues more frequently during the startup sequence [13][22].

Beyond boot failures, the operating system has faced internal service malfunctions. Users have encountered sign-in failures caused by authentication service errors identified by Microsoft telemetry [1][3][10]. Additionally, some systems failed to verify their activation status correctly [2]. These licensing bugs are particularly prevalent during license migrations involving the CLIP / online entitlement activation server [11].

Issue Category Common Symptoms Technical Impact
System Startup Black screens and boot loops [5][6] UNMOUNTABLE_BOOT_VOLUME error [12][14]
Authentication Sign-in and user access failures [1][10] Broken authentication services [1][3]
Licensing Incorrect activation status [2][9] License migration failure [11]

These combined issues have created a scenario where users may be locked out of their accounts or find their operating system incorrectly reporting licensing malfunctions [1][2]. The impact ranges from minor inconveniences during login to total system failure requiring manual intervention [22][47].

Root Causes / Analysis

The recent wave of Windows 11 instability is not the result of a single error, but rather a convergence of update conflicts and security certificate transitions. Analysis of system telemetry and official release notes indicates four primary drivers behind these failures.

December 2025 Rollback Conflicts

A significant number of boot failures are linked to an improper state caused by failed attempts to install or roll back the December 2025 security update [2][15]. When these previous updates did not complete successfully, they left residual configurations that conflicted with subsequent patches [15]. This specific issue has been identified as a primary cause for boot failures on business PCs [55].

The Impact of KB5074109

The cumulative update KB5074109, released on January 13, 2026, has been directly linked to unusable boot volumes [28][52]. This update appears to have introduced critical errors in the startup sequence for a subset of devices [8]. These failures are most prevalent on systems running Windows 11 versions 24H2 and 25H2 [11][12].

Secure Boot Certificate Transitions

Modern Windows systems are currently undergoing a multi-year transition to update Secure Boot certificates [4][9]. Industry reports indicate that the January 2026 updates caused conflicts between firmware and the operating system during this certificate verification process [23][5].

Success in this transition requires the system to recognize the new Microsoft Corporation KEK 2K CA 2023 signature [14]. The deadline for these updates is set for June 2026, but the phased rollout has already caused startup failures on devices with older UEFI configurations [4][13].

Driver and Hardware Regressions

In addition to boot loops, some updates have introduced hardware regressions. Specifically, reports surfaced around January 26, 2026, indicating that update KB5074109 caused modem functionality to break for various users [56]. While these hardware issues do not always prevent booting, they contribute to the overall system instability reported during this update cycle [56].

Evidence & Reality Check

Microsoft telemetry and technician reports confirm that these issues are widespread across specific versions of Windows 11 [10][23]. While the KB5074105 update was released specifically to resolve these boot, sign-in, and activation failures [1][6], some users continue to report difficulties.

Note: Unverified reports from community forums suggest that boot failures may persist on some hardware configurations even after applying available out-of-band updates [27].

Analysts observe that the complexity of the Secure Boot database update, combined with the "improper state" left by the December 2025 cycle, created a high-risk environment for the January 2026 patches [15][23]. Data suggest that the interaction between legacy UEFI certificates and new security requirements is a primary point of failure for older hardware [4][23].

Evidence & Reality Check

Microsoft has publicly acknowledged performance and reliability "pain points" within Windows 11 [5][10]. To address these concerns, the company is reportedly utilizing an internal engineering strategy known as swarming [1][6][7]. This process involves redirecting engineering resources away from developing new features to focus on resolving long-standing system glitches and stability issues [1][2][10].

Reports indicate that Microsoft leadership, including Pavan Davuluri, has committed to making 2026 a year focused on performance, reliability, and the overall user experience [5][14]. While some improvements are confirmed, rumors suggest that the most significant performance resolutions may roll out gradually over the coming months of 2026 [4].

Official documentation and technical logs confirm that recent updates have targeted specific system failures. The following table summarizes the status of documented issues:

Issue Status Source
iSCSI boot failures Resolved (Inaccessible Boot Device) [3]
explorer.exe login hangs Resolved (Taskbar now appears) [8]
0x803F8001 error Identified (Notepad & Xbox apps) [10]
Shutdown failures Addressed via out-of-band patches [9][11][13]

The necessity for this renewed focus on stability followed a series of software update complications in early 2026. In January 2026, a standard update reportedly caused system shutdown issues and application crashes for services such as OneDrive and Dropbox [9][11]. Microsoft was forced to issue emergency out-of-band patches to mitigate these errors [9][11].

The KB5074105 update is part of this broader stabilization effort [14]. Technical documentation indicates this specific update provides resolutions for boot-related failures and cycles [15]. It also addresses conflicts that previously caused sign-in and activation issues on some hardware configurations [2][15].

Industry observations suggest that these steps are part of a larger initiative to rebuild user trust in the Windows ecosystem [2][55]. While these updates address critical bugs, experts suggest that users should continue to monitor system performance, as the full "swarming" effort is expected to continue throughout 2026 [1][14].

Self-Check / Diagnosis

To determine if your system is impacted by the recent update issues or if it requires the KB5074105 resolution, you should look for specific error codes and system identifiers.

1. Verify your Windows Build number

The primary way to confirm if your system has the latest fixes is by checking the OS build version. Microsoft has released specific builds to the Release Preview Channel to address boot and sign-in failures [3].

  • Target Builds: Ensure your system is running Build 26100.7701 or 26200.7701 [3].
  • How to check: Open Settings > System > About. Scroll down to Windows specifications to locate the OS build number.

2. Identify the 'UNMOUNTABLE_BOOT_VOLUME' stop code

The most common symptom of a failed January update is a system crash during the startup sequence. You should monitor your screen for a Black Screen of Death (BSOD) displaying a specific technical identifier [13][24].

Symptom Error Code / Behavior
System Crash UNMOUNTABLE_BOOT_VOLUME [23][58][59]
iSCSI Failure Inaccessible Boot Device [3]
Visual State Black screen or stuck at startup logo [13][24]

If your PC displays the UNMOUNTABLE_BOOT_VOLUME code, it indicates that the operating system is unable to mount the boot drive following the update [15][47].

3. Check for hardware-specific regressions

Some symptoms are specific to certain hardware configurations or laptop brands.

  • Integrated Cameras: Users with Acer laptops should check if their integrated cameras are functioning. Reports indicate that the KB5074105 update can cause these cameras to blink incessantly or display a "hardware failure" error [33].
  • Taskbar Disappearance: If you can log in but the taskbar does not appear, this may be due to explorer.exe hanging [3]. This often occurs during the first login after an update due to startup app conflicts [3].
  • iSCSI Boot: If your environment relies on iSCSI for booting and the process fails, it is likely tied to the boot device errors addressed in the latest builds [3].

4. Monitor Secure Boot signatures

For advanced users, checking the Secure Boot signature version can confirm if security updates have been applied. The update transitions systems from the 2011 signed bootmgfw.efi to the 2023 version [5]. This change is typically required for devices utilizing the UEFI CA 2023 certificate [5].

Warning: If your system is currently in a boot loop with a black screen, do not attempt to force multiple restarts, as this may complicate the recovery of the boot volume [24][59].

Solutions / What to Do

To address the persistent stability and licensing issues in Windows 11, users can take several specific actions depending on whether their system is currently bootable. These steps focus on deploying the KB5074105 update or removing problematic previous patches.

Method 1: Manually Check for Windows Updates

The most direct solution for resolving boot loops, sign-in failures, and activation errors is the installation of KB5074105 [1][3][5]. This update is specifically designed to mitigate authentication service errors and system startup failures [4][6].

  • Open Settings and navigate to Windows Update.
  • Select Check for updates to locate the official release.
  • If the update appears as an "Optional Quality Update," select Download and install to apply the fixes for system stability and license migration [3][11].

Method 2: Manual Installation via Microsoft Update Catalog

In cases where the automated Windows Update service fails to retrieve or apply the patch, a manual installation may be necessary. Users can potentially resolve these issues by downloading the standalone installer directly.

Component Benefit of Manual Installation
System Stability Bypasses potential errors in the automated update service [2][11].
Activation Fix Directly applies patches for the CLIP and online entitlement servers [11][15].
Boot Reliability Ensures the technical improvements for startup sequences are fully applied [6][8].

Method 3: Utilize Windows Recovery Environment (WinRE)

If a system is unable to reach the desktop due to a boot failure, Microsoft-confirmed guidance involves using the Windows Recovery Environment (WinRE) [14]. This environment allows for the removal of recent updates that may be causing the instability.

  • Uninstall Updates: Within WinRE, users can attempt to uninstall the latest quality update to restore basic boot functionality [14].
  • Identify Problematic Patches: Some systems have experienced failures specifically tied to KB5074109 [10].
  • Error Monitoring: It is important to note that uninstallation of certain patches, such as KB5074109, can potentially fail with error 0x800f0905 [10].
  • Advanced Recovery: If WinRE is unable to repair the boot process, an ISO reinstallation of the operating system may be required to resolve the error [13].

Risks and Limitations

While these methods are intended to restore system health, they are not without potential complications. Using the Windows Recovery Environment requires careful navigation of system menus, and some recovery operations may not succeed if system files are heavily corrupted [13].

Furthermore, while KB5074105 addresses core licensing malfunctions, it may not resolve activation issues caused by hardware changes or invalid product keys [9][15]. If manual uninstallation of previous updates fails with error codes like 0x800f0905, a System Restore to a previous point in time is often the next recommended step [10].

Risks, Limits, and When to Stop

While KB5074105 is designed to address critical system failures, it is currently classified as an optional preview release for Windows 11 versions 24H2 and 25H2 [7]. As a preview build, it may potentially introduce new software regressions that have not yet been fully addressed in standard monthly security updates [7][14].

Potential Software Regressions

Community reports and technical analysis suggest that some users may experience side effects after installing this update. These reported issues include:

  • Camera Malfunctions: Specific reports indicate that laptop cameras, particularly on Acer devices, may stop functioning [12][33]. Affected hardware might display a "hardware failure" error or exhibit incessant blinking [12].
  • UI and Lock Screen Instability: There are unverified reports of system instability, including lock screen widget crashes and unresponsive interface elements [10][33][38].
  • General Performance Issues: Some users have reported broader system instability following the installation of KB5074105, suggesting that the patch may conflict with certain hardware configurations [14][38].

Comparison of Update Status and Risks

Feature Status Risk Level
Update Type Optional Preview Release [7] Moderate
Boot Fixes Addresses startup and sign-in failures [1][2][11] Low (Targeted Fix)
Hardware Compatibility Potential regressions with webcams and lock screens [33][49] Moderate
System Stability Reported cases of post-install instability [14][38] Variable

When to Seek Professional Diagnosis

Software updates can occasionally expose underlying hardware vulnerabilities. If you experience persistent boot failures that continue even after attempting a software rollback or uninstalling the update, the issue might not be limited to the operating system code.

In many cases, recurring startup cycles or "boot loops" can indicate potential issues with:

  • Storage Health: A degrading SSD or HDD can cause symptoms that mimic a corrupt update.
  • Memory (RAM) Stability: Corrupt memory modules often lead to crashes during high-activity sequences like system startup or user authentication.

If standard recovery tools—such as System Restore or Uninstall Updates—fail to stabilize the computer, it is advisable to stop DIY troubleshooting. Repeatedly forcing restarts or attempting multiple re-installations can potentially lead to data loss if the underlying cause is related to hardware failure. In such scenarios, a professional hardware diagnostic is generally the safest course of action to prevent further damage.

Note: If you are not currently experiencing the specific boot, sign-in, or activation issues addressed by this patch, it may be safer to wait for the final, non-preview version of the update [7][10].

FAQ

Why did my dial-up modem or telephony system stop working?

The loss of functionality is likely due to the removal of legacy drivers in update KB5074109 [15]. This update specifically uninstalls driver files such as agrsm64.sys, agrsm.sys, smserl64.sys, and smserial.sys [15]. These changes render certain 56k modems non-functional, a change confirmed by reports on Microsoft Q&A and community forums [5].

Will update KB5074105 fix my NVIDIA GPU performance drops?

Update KB5074105 is primarily designed to resolve core stability issues, including boot loops, sign-in failures, and explorer.exe hangs [1][3][12]. While it improves general system reliability, it may not directly address specific NVIDIA GPU performance issues [6][9]. Rumors suggest that recent updates have caused gaming performance to drop by up to 20 FPS, particularly on systems with NVIDIA GeForce RTX graphics cards [2][7][39].

Is the KB5074105 update mandatory for all users?

Currently, this update is released to the Release Preview Channel, which generally makes it an optional preview rather than a mandatory installation [3]. It is highly recommended for users experiencing persistent Inaccessible Boot Device errors or Windows license migration failures [1][4]. If your system is stable, you may choose to wait until these fixes are integrated into a standard cumulative update [3][10].

Why is my taskbar not appearing after I log in?

This issue is often caused by explorer.exe hanging during the first login process, frequently due to conflicts with startup apps [3]. Update KB5074105 specifically addresses this bug to ensure the taskbar and user interface load correctly [3]. Technical improvements in this patch aim to correct authentication service errors identified by Microsoft telemetry [11].

How does this update handle Windows activation issues?

The update provides a resolution for failures in Windows license migration related to the CLIP / online entitlement activation server [4][13]. It is specifically designed to fix issues that occur during Windows 11 upgrades where the system fails to verify legitimate licenses [4][13]. This patch ensures the activation service functions as expected during the system boot and sign-in process [5][8].

Summary / Key Takeaways

The KB5074105 update is a critical stabilization patch released to address core system failures within the Windows 11 environment [4][7][15]. It targets specific errors identified through telemetry to improve overall system reliability and performance [5][64].

  • System Stability: The update serves as a primary resolution for users experiencing persistent boot failures and startup loops [1][2][13].
  • Authentication and Access: It mitigates sign-in failures and rejected credential errors that prevented users from accessing their accounts [5][11][14].
  • Licensing and Activation: The patch corrects activation malfunctions and license migration issues related to the CLIP and online entitlement servers [3][10][12].
  • Targeted Versions: This stabilization effort specifically supports Windows 11 24H2 and 25H2 environments [60].

While this update addresses several critical bugs, professional intervention is often safer than repeated manual recovery attempts for critical system failures.

If you’re unsure, it’s usually cheaper to ask someone once than to fix a mistake later.

Quellen

[1] Microsoft: Windows 11 KB5074105 update fixes boot, sign-in, and activation issues

[2] Microsoft Support: Windows 11 Update KB5074105: Resolution for Boot, Sign-in, and Activation Issues

[3] Microsoft Windows Insider Blog: Releasing Windows 11 Builds 26100.7701 and 26200.7701 to the Release Preview ...

[4] ASUS Global Support: Windows Secure Boot certificate expiration and certificates updates

[5] Microsoft Support: Windows 11 KB5074105 update fixes boot, sign-in, and activation issues

[6] Sportskeeda: Microsoft says Windows 11's "pain points" will be addressed in 2026

[7] Windows Latest: Microsoft reportedly admits Windows 11 went off track, cuts back Copilot, and...

[8] The Verge: Microsoft is working to rebuild trust in Windows

[9] GB News: Microsoft wants to fix everything you hate about Windows 11 with major update...

[10] 80 Level: Microsoft Acknowledges Windows 11's Issues, Promises to Fix Them

[11] BleepingComputer: Windows 11 KB5074105 update fixes boot, sign-in, and activation issues

[12] SoftAntenna: Windows 11 Version 25H2/24H2 Preview Update KB5074105 Released - Many new fea...

[13] heise online: Windows Update Preview: Cross-device continuation and MIDI 2.0

[14] Windows Central: 8 new Windows 11 features expected to arrive with the February 2026 update

[15] BleepingComputer: Microsoft links Windows 11 boot failures to failed December 2025 update

[21] The Register: Microsoft probes Windows 11 boot failures tied to January security updates

[22] SlashGear: This Windows 11 Update Could Seriously Screw Up Your PC

[23] PC-Doctor, Inc.: Windows 11 Boot Failures After Recent Updates: What Technicians Should Check ...

[24] MundoWin: Windows 11 won't start after the latest update: what's happening and how to t...

[27] BGR: New Windows 11 Security Update Might Have Killed Some Computers

[28] The Financial Express: Downloaded the latest Windows 11 January 2026 update? Microsoft has a WARNING...

[30] 3DNews: Microsoft fixes login and boot crashes in latest Windows 11 update

[33] SoftAntenna: Warning: Windows 11 Optional Update KB5074105 Causing Multiple Issues - Camer...

[38] Cultura Informática: Windows 11 KB5074105 has introduced a new security feature

[39] TecnoBits: Emergency update for Windows 11 due to critical bugs in January

[44] GameStar: Windows 11: The problems in the January update are probably even greater than...

[47] ZDNET: Why you need Microsoft's new emergency Windows patch - and the black-screen b...

[49] Hipertextual: Windows 11 Continues to Fail: Latest Update Breaks Webcam and System

[51] COMPUTER BILD: Windows 11: After January Patch, PCs No Longer Start

[52] WinFuture: Windows 11 Chaos: Boot Volume Unusable After Patch Day Updates

[55] The Verge: Microsoft is working to rebuild trust in Windows

[56] Windows Central: Microsoft issues emergency out-of-band update for Windows 11 to address major...

[58] The Register: Microsoft probes Windows 11 boot failures tied to January security updates

[59] Windows Central: Windows 11’s January update is breaking PCs — here’s how to fix your boot issue

[60] Tom's Hardware: Windows 11 KB5074105 update fixes boot, sign-in, and activation issues

[64] Microsoft Technical Support / Tech Media: Windows 11 KB5074105: Resolving System Startup and Activation Failures

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