Yes—Microsoft received a limited number of reports that the January 13, 2026 security update, KB5074109, left some Windows 11 24H2 and 25H2 devices unable to start, sometimes showing UNMOUNTABLE_BOOT_VOLUME. It was not a universal failure. If your PC is affected, try removing the latest quality update from Windows Recovery Environment (WinRE) before considering a reset or clean installation.
What happened with KB5074109?
KB5074109 was the cumulative security update released on January 13, 2026 for Windows 11 versions 24H2 and 25H2. It moved 24H2 to build 26100.7623 and 25H2 to build 26200.7623. Microsoft’s package also included servicing-stack changes and Secure Boot certificate-targeting changes. See Microsoft’s release documentation at KB5074109 release notes.
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Microsoft received a limited number of reports that devices failed to boot after KB5074109 or subsequent updates. Secondary reports identified the stop code UNMOUNTABLE_BOOT_VOLUME. That scope means some device and configuration combinations were affected—not every 24H2 or 25H2 computer.
The available reports do not establish a single technical cause. The stop code means Windows could not mount or access the system volume during startup. An update regression is one possibility; storage-driver or controller incompatibility, filesystem damage, broken boot files, and an underlying drive problem are others. The message alone does not prove that an SSD or hard drive has physically failed.
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Is the boot problem fixed now?
KB5074109 is no longer the current Windows 11 update. Microsoft released two January out-of-band packages:
| Update | Date and scope | What is documented |
|---|---|---|
| KB5077744 | January 17, 2026; 24H2 and 25H2 | Addressed earlier January problems such as remote-connection authentication and hibernation issues. Secondary reporting did not show it as a confirmed fix for the boot failures. |
| KB5078127 | January 24, 2026; builds 26100.7628 and 26200.7628 | Included the January 13 security update and January 17 OOB package, and resolved documented remote-connection and cloud-backed-storage issues. Microsoft’s notes are at KB5078127 release notes. |
It is not safe to describe KB5078127 as a universal cure for every UNMOUNTABLE_BOOT_VOLUME incident. Microsoft’s release-health material does not clearly provide a dedicated resolution entry for those specific boot-failure reports. Later cumulative updates incorporated improvements from the January packages, so a stable system should generally receive the latest supported update after you check the current Windows release-health hub.
How to recover a PC that will not boot
1. Reduce the risk of further damage
- Do not repeatedly hard-power-cycle the computer unless it is completely unresponsive.
- Disconnect nonessential USB devices, docks, external drives, and other peripherals.
- Before destructive repairs, plan how you will copy important files from recovery media or another computer.
2. Enter Windows Recovery Environment
After repeated failed starts, Windows commonly opens WinRE automatically. If it does not, start from Windows installation or recovery media created from Microsoft’s Windows 11 download page. If BitLocker is enabled, WinRE may request the recovery key. Retrieve it from your Microsoft account, your organization’s Entra ID or Active Directory records, or your printed or exported recovery documentation. Do not disable BitLocker casually.
3. Remove the latest quality update
- Select Troubleshoot.
- Choose Advanced options.
- Select Uninstall Updates.
- Choose Uninstall latest quality update.
- Restart and test Windows.
Because cumulative updates supersede one another, WinRE may show a later package rather than KB5074109 by name. Removing the latest quality update can therefore roll back a superseding cumulative update. Microsoft also warns that uninstalling the combined KB5074109 package with wusa.exe /uninstall may fail because it includes a servicing-stack update; WinRE’s uninstall option is the safer first choice.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errors4. Try Startup Repair
Use Troubleshoot → Advanced options → Startup Repair. It can repair boot-configuration problems, but it may not remove a faulty cumulative update.
5. Try System Restore
Use Troubleshoot → Advanced options → System Restore if a suitable restore point exists. Restore may be disabled, unavailable, or unable to reverse every update change.
6. Try Safe Mode
Choose Troubleshoot → Advanced options → Startup Settings → Restart, then select Safe Mode. If Windows starts there, remove the recent update through recovery or installed-update controls and back up your data before a normal reboot.
7. Use DISM only when you can identify the correct volume and package
In WinRE, Windows is not always mounted as C:. Open Command Prompt and identify the Windows volume:
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exitThen inspect installed packages, substituting the correct drive letter:
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dism /Image:C: /Get-PackagesOnly an exact package name from that output should be removed:
dism /Image:C: /Remove-Package /PackageName:<exact-package-name>Do not guess the package name. An incorrect DISM operation can make recovery more difficult.
8. Preserve data before a reset or reinstall
If the system remains unbootable, copy files using WinRE, a recovery drive, a Linux live environment, or by connecting the storage drive to another computer. Consider Reset this PC, an in-place repair installation, OEM recovery media, or a clean installation only after update removal and data recovery attempts. Reset and clean installation can cause data loss.
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How to confirm whether KB5074109 is installed
Use Windows Settings
- Open Settings.
- Select Windows Update.
- Open Update history.
- Under Quality Updates, look for KB5074109.
Check the version and build
Run winver (or open Settings → System → About) to identify the Windows version and build. The command systeminfo provides additional system details.
Use a command
Command Prompt:
wmic qfe | findstr 5074109WMIC may be absent or deprecated on newer installations. PowerShell is the better alternative:
Get-HotFix -Id KB5074109When the update may not be the cause
- The drive is missing from UEFI or firmware storage listings.
- SMART diagnostics report errors or the drive repeatedly disconnects.
- The PC had boot problems before January 13, 2026.
- The same failure remains after removing the latest quality update.
- The machine recently experienced power loss, filesystem corruption, malware, a storage upgrade, or a loose drive connection.
These signs increase the likelihood of hardware, filesystem, firmware, or driver trouble. Protect the data first and use the device maker’s diagnostics or qualified service if the drive is not detected.
Do not confuse this with other January 2026 bugs
January updates produced several separately tracked problems:
- Remote Desktop, Azure Virtual Desktop, and Windows 365 credential prompts or authentication failures.
- Applications freezing while opening or saving files in OneDrive, Dropbox, and other cloud-backed locations.
- Hibernation or shutdown failures.
- Windows Recovery Environment USB-input problems reported around other update activity.
- Secure Boot certificate deployment and expiration concerns.
Microsoft documented several remote-connection and cloud-storage issues as resolved by KB5078127, including entries for Windows 11 25H2 and Windows 11 24H2. Those resolutions do not prove that every boot failure was resolved. Microsoft also warned that older Secure Boot certificates would begin expiring in June 2026; that security-maintenance issue should not automatically be treated as the cause of the January stop code. The relevant later notice is Microsoft’s Secure Boot guidance.
Guidance for managed PCs
Businesses may deploy updates through Intune, Windows Autopatch, WSUS, Configuration Manager, or another patch system. Do not uninstall updates across an entire estate based only on anecdotal reports. First identify affected models, Windows builds, update rings, timing, and failure rates; preserve logs and coordinate with Microsoft Support. Microsoft provides specific guidance for Intune and Windows Autopatch administrators in the KB5078127 documentation.
Quick Recap
Recovery checklist
- Record the Windows version, build, update history, and stop code.
- Disconnect unnecessary peripherals.
- Locate the BitLocker recovery key before changing recovery settings.
- Enter WinRE and uninstall the latest quality update.
- Try Startup Repair, System Restore, and Safe Mode in that order.
- Use DISM only after identifying the correct Windows volume and exact package name.
- Back up files before Reset this PC or reinstalling Windows.
- After the system is stable, check Microsoft’s current release-health guidance and install the latest supported cumulative update.
- Escalate to Microsoft, the OEM, or a qualified technician if the drive is absent, data is at risk, or recovery repeatedly fails.
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