[Summary]
Some PCs that have installed KB5074109 (OS Build 26200.7623 and 26100.7623) may experience boot failures, and Microsoft is investigating.
* The following is a translation of the X (formerly Twitter) post.
Microsoft is investigating reports that some systems are failing to boot after the Windows 11, January 2026 update.
"Microsoft has received reports of limited cases where devices fail to boot with the stop code 'UNMOUNTABLE_BOOT_VOLUME' after installing the January 2026 Windows security update," it explained.
Microsoft is still investigating whether the issue is caused by the Windows update. The company has asked users to submit feedback to facilitate the investigation.
Previously, Microsoft also asked users to uninstall the January 2026 update when Outlook was not working. Earlier today, it released a second emergency update for Windows 11 to address fundamental issues.
https://x.com/WindowsLatest/status/2015479724689314153
