If you have downloaded the latest security updates from the January 2026 patch, you could be in trouble. Microsoft has acknowledged a serious issue with its January 2026 security update for Windows 11, confirming that a limited number of devices are failing to boot properly after installation. The problem, which surfaced following the release on January 13, adds to a string of headaches users have faced this month with cumulative updates.
The affected update, identified as KB5074109, targets Windows 11 versions 24H2 and 25H2 on physical PCs (non-cloud versions). Microsoft says it is receiving reports of devices displaying a black screen of death (BSOD) with the stop code UNMOUNTABLE_BOOT_VOLUME. Users see the familiar message: “Your device ran into a problem and needs to restart. You can restart.” However, the system enters a loop or recovery state and cannot complete startup, leaving the PC effectively unbootable without intervention.
Windows 11 update prevents PC bootup process
In confirmed cases, the boot failure occurs post-update, with the machine stuck at a black screen and unable to proceed to the login or desktop. Microsoft describes the impact as limited, affecting only a subset of devices, though the exact number of users impacted remains unclear. The issue appears tied to physical hardware configurations rather than virtual machines, and no widespread enterprise or specific hardware patterns have been publicly detailed yet.
This system boot problem marks the latest escalation in what has been described as a troubled January Patch Tuesday cycle. Earlier in the month, the same update batch triggered:
– Shutdown and hibernate failures on Windows 11 version 23H2,
– Remote Desktop sign-in issues on 24H2 and 25H2,
– Inoperability of cloud-backed applications like Outlook, Dropbox, and OneDrive,
All these issues have prompted Microsoft to issue multiple emergency out-of-band fixes (including updates like KB5078127 and others).
Microsoft’s recovery guide: What to do if you can’t start your PC
Microsoft is actively investigating the boot failure reports and working on potential fixes or additional workarounds. In the interim, the company advises affected users to manually recover their systems by accessing the Windows Recovery Environment (WinRE) and uninstalling the problematic January quality update.
The steps that are generally involved include:
– Forcing the PC into WinRE (often by interrupting boot multiple times or using recovery media),
– Navigating to Troubleshoot > Advanced options > Uninstall Updates,
– Selecting “Uninstall quality update” to remove KB5074109.
The detailed recovery instructions are available on Microsoft’s support pages and in community guides. While the update delivered legitimate security improvements and fixes (such as better NPU battery management), the recurring quality issues have drawn criticism, with calls for Microsoft to improve its pre-release testing processes.
