Microsoft suspects some PCs might not boot after Windows 11 January 2026 Update
Summary
Windows Latest reports that the Windows 11 January 2026 Update KB5074109 can cause some devices to fail boot with UNMOUNTABLE_BOOT_VOLUME, limited to certain hardware and builds (24H2/25H2). Microsoft recommends recovery options and has issued an emergency update KB5078127 to address related issues; admins should verify build numbers (26200.7623) and prepare rollback and recovery plans rather than uninstalling the update.