By Lawrence Abrams
Publication Date: 2026-01-25 13:20:00
Microsoft is investigating reports that some Windows 11 devices are failing to boot with “UNMOUNTABLE_BOOT_VOLUME” errors after installing the January 2026 Patch Tuesday security updates.
The issue affects Windows 11 version 25H2 and all editions of Windows 11 version 24H2 after installing the KB5074109 cumulative update released as part of this month’s updates.
According to Microsoft, some customers have reported that their systems fail to start and display a stop error during boot.
“Microsoft has received a limited number of reports of an issue in which devices are failing to boot with stop code ‘UNMOUNTABLE_BOOT_VOLUME’, after installing the January 2026 Windows security update (the Originating KBs listed above), released January 13, 2026, and later updates,” Microsoft stated.
The company says that affected devices will show a black Windows crash screen stating, “Your device ran into a problem and needs a restart. You can restart.”
Microsoft says the…
