Why are some Windows 11 PCs unable to boot after the January update?

A separate bug from the January update causes a black screen and an "unmountable boot volume" error on certain Windows 11 versions, preventing them from booting up.

What is Microsoft doing about the Windows boot failure bug?

Microsoft has acknowledged the reports of devices failing to boot and is currently investigating the problem, although a fix has not yet been released.

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Windows Bugged: Patch Fixes Cloud, Breaks Boot

Q: What does Microsoft's emergency patch KB5078127 fix?

The emergency patch KB5078127 resolves issues with opening and saving files to cloud services like OneDrive and Dropbox, which were introduced by the January 2026 Patch Tuesday update.

26 Jan

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Summary

Microsoft issued an emergency patch for cloud storage issues.
A separate bug prevents some Windows PCs from booting.
The January update introduced numerous glitches requiring fixes.

Windows Bugged: Patch Fixes Cloud, Breaks Boot

Microsoft has issued an urgent out-of-band patch, KB5078127, to address critical bugs stemming from its January 2026 Patch Tuesday update. This patch specifically resolves an issue that prevented applications, including Outlook, from opening or saving files to cloud services like OneDrive and Dropbox.

The emergency update also incorporates fixes for remote connection problems and Secure Launch issues previously addressed on January 17th. Users encountering difficulties with cloud storage are advised to install KB5078127 and restart their systems.

However, the bug situation for Windows users is far from resolved. A distinct glitch, also linked to the January update, is reportedly causing a black screen and an "unmountable boot volume" error on a limited number of Windows 11 PCs (versions 25H2 and 24H2), rendering them unbootable.