Microsoft investigates startup and stability issues affecting recent Windows 11 versions
Microsoft is investigating serious problems linked to its January 2026 security update for Windows 11 after reports of systems failing to start correctly. The update, which was meant to strengthen security, has instead left some users unable to boot their devices.
The issue is tied to update KB5074109, released for Windows 11 versions 25H2 and 24H2. Shortly after installation, affected systems began showing critical startup errors, including boot loops and black screens. In some cases, devices display an UNMOUNTABLE_BOOT_VOLUME error and never reach the login screen.
Microsoft has acknowledged the problem and confirmed receiving a limited number of reports where devices cannot complete startup. So far, the issue appears to affect physical machines only, with virtual environments remaining unaffected. For impacted users, access to the operating system is often lost entirely, requiring recovery tools to remove the update.
Even on systems that manage to boot, the update has caused widespread stability concerns. Users report random freezes, display issues, and conflicts with graphics drivers, particularly during GPU-intensive tasks. Some applications become unresponsive without triggering a crash or error message, leaving systems stuck until a forced restart.
The update has also disrupted productivity and enterprise services. Microsoft confirmed that credential prompts for certain cloud and remote desktop services were broken, temporarily preventing users from connecting. Outlook Classic users have also reported freezes and sync problems after startup.
What users should do now
- Uninstall the latest update using the Windows Recovery Environment if the system won’t boot
- Roll back KB5074109 or pause updates on unstable systems
- Delay installing the update until Microsoft releases a permanent fix
Microsoft continues to investigate the root cause of these failures. Until a comprehensive resolution is available, users and administrators are advised to approach the January update with caution, especially on production systems.
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