Windows 11 Patch Tuesday horrors continue as some PCs now cannot boot

The January 2026 Patch Tuesday update for Windows 11 keeps on giving users headaches. Following reports about frozen apps, broken apps, and the rather hilarious inability to shut down PCs, which are now said to be resolved after the second emergency OOB update (KB5078127, KB5078132) users are now facing a much more serious issue where affected computers simply refuse to boot and show an "UNMOUNTABLE_BOOT_VOLUME" error.

The problem is as terrible as it sounds, and Microsoft has already confirmed it. In the Admin Center, the company issued a notification that it had received "a limited number of reports" where computers cannot boot and show a dreadful "UNMOUNTABLE_BOOT_VOLUME" error after applying KB5074109 from January 13 and later (including the latest out-of-band update).

Here is how Microsoft describes it:

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. Affected devices show a black screen with the message “Your device ran into a problem and needs a restart. You can restart.” At this stage, the device cannot complete startup and requires manual recovery steps.

At this point, affected customers should apply "manual recovery steps" to bring their PCs back to life, although no specific steps were provided by Microsoft. The company only says that the problem affects local machines with client versions of Windows 11 25H2 and 24H2. The company is investigating the problem and will share more information once it has it.

Interestingly, Microsoft came up with a technical solution for scenarios like this. In 2024, Microsoft announced Quick Machine Recovery (and even redesigned the legendary Blue Screen of Death), a mechanism that allows applying remedies for outages and critical bugs within the Windows Recovery Environment or WinRE. At this point, it does not seem to be much of help, as Microsoft is still investigating the root cause of the problem.

Via AskWoody

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Posted Monday 26 January 2026 at 5:07 am AEST (my time).

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