Windows 11 January 2026 updates may cause boot failures on some PCs. Microsoft is investigating issues linked to KB5074109.

Windows 11 KB5074109 (January 2026 Update) is causing major issues on some PCs, and Microsoft has more details to share.

Microsoft is investigating reports that some Windows 11 devices are failing to boot with "UNMOUNTABLE_BOOT_VOLUME" errors ...

Round and round we go.

It's not just January's one.

Microsoft has linked recent reports of Windows 11 boot failures after installing the January 2026 updates to previously failed attempts to install the December 2025 security update, which left systems ...

The most recent January Windows Update is broken on a number of PCs, but at least virtual machines don't seem to be impacted.

Microsoft is investigating reports of serious boot failures affecting Windows 11 devices following the January 2026 security ...