Microsoft is actively investigating reports that a number of Windows 11 devices are failing to start properly after installing the January 2026 Patch Tuesday updates, causing significant concern among both consumers and IT professionals worldwide.
What’s Happening?
Following the rollout of the January 2026 cumulative security update — specifically KB5074109, released on January 13 — a limited number of Windows 11 PCs have experienced boot failures. Affected systems display a Blue Screen of Death (BSOD) with the stop code UNMOUNTABLE_BOOT_VOLUME, after which the machines are unable to complete the startup process without manual intervention or recovery tools.
In many cases, users report seeing a black crash screen with a message indicating that the device “ran into a problem and needs a restart,” but restarting does not resolve the issue. These failures seem confined to physical devices — virtual machines are not currently showing the same behavior — though the exact number of impacted systems remains unclear.
Who Is Affected?
Microsoft says the issue impacts devices running both Windows 11 version 25H2 and all editions of version 24H2 that have installed the latest update. These are among the most widely deployed Windows 11 versions, meaning even a small percentage of failures can cause disproportionate disruption, especially in larger enterprise environments where update deployment is managed centrally.
Microsoft’s Response
In response to the reports, Microsoft has acknowledged the problem and launched an investigation to determine whether this behavior is a regression caused by the update itself. While the company has not yet confirmed a root cause, it has urged affected users and system administrators to submit detailed feedback via the Feedback Hub to help with diagnostics.
Broader Issues With This Update
This is not the only glitch tied to the January 2026 Patch Tuesday updates. Other reports have surfaced of PCs failing to shut down or enter sleep mode properly, applications freezing (including Outlook), and peripheral functionality breaking on some hardware configurations. Microsoft has already issued emergency “out-of-band” updates to address several of these problems, but those fixes have at times introduced additional issues, prompting further patches.
What Users Should Do
If your PC fails to boot after applying updates:
- Do not force repeated restarts — this can exacerbate file system corruption.
- Boot into Windows Recovery Environment and attempt a repair using Startup Repair or command-line utilities if possible.
- Track official updates via Windows Update and the Windows Release Health Dashboard for guidance from Microsoft.
- IT admins should gather logs and user reports through corporate management tools and submit feedback to Microsoft.
The timing of these issues — coming early in the year’s update cycle — highlights ongoing challenges with Windows Update quality assurance. While security patches are essential, unexpected regressions that prevent devices from booting or functioning normally are serious setbacks, especially for business users who depend on reliable systems. Microsoft’s continued investigation and responsive patching will be key to restoring confidence and stability across the Windows 11 ecosystem.
