Microsoft confirmed that its January 2026 security updates caused a limited number of physical Windows 11 devices to fail to start, showing a black screen with the message "Your device ran into a problem and needs a restart" and the stop code UNMOUNTABLE_BOOT_VOLUME. This affects Windows 11 versions 25H2 and 24H2.
Why this happens
The January 2026 update introduced a problem specifically affecting how certain systems mount their boot volume during startup, causing affected devices to fail before completing the boot process. Microsoft has acknowledged this is tied to the update itself rather than unrelated hardware failures, though it affects only a limited subset of physical devices (not virtual machines).
The fix: uninstall the update from the Recovery Environment
Since affected devices can't reach the desktop to uninstall the update normally, this needs to be done through the Windows Recovery Environment (WinRE):
- If your PC is stuck in a boot loop, it should automatically enter the Recovery Environment after a few failed attempts. If not, force this by holding the power button to shut down during boot, three times in a row.
- Once in the Recovery Environment, click Troubleshoot
- Click Advanced options
- Click Uninstall Updates
- Select "Uninstall latest quality update"
- Sign in with your administrator credentials if prompted
- Click Uninstall quality update to confirm
After this completes, the device should boot normally again, now without the problematic update installed.
If you can't reach the Recovery Environment this way: some systems may need to boot from Windows installation media (a USB recovery drive) to access the same recovery tools. If you don't already have one, this needs to be created on a different, working computer — worth keeping one on hand generally as a precaution for situations exactly like this.
What to do after recovering
Once your system is back up and stable:
- Pause Windows Update temporarily (Settings → Windows Update → Pause updates) until Microsoft ships a corrected version of the patch, to avoid reinstalling the same problematic update automatically.
- Check Windows Update regularly for the corrected patch — Microsoft has confirmed it's actively working on a fix, and once available, it should be safe to update normally again.
- Back up important files while your system is stable, as a general precaution — not strictly required by this specific issue, but always good practice after any boot-related scare.
If you manage multiple machines
If you're responsible for several computers in a small office and this is a known risk for your fleet, consider deferring feature and quality updates briefly on non-critical machines until any acknowledged issue like this has had time to be addressed, rather than auto-installing every update immediately across all devices at once.