Microsoft confirms some PCs cannot boot after recent update, explains what happened

January 2026 was nothing but a disaster for Windows, with Microsoft confirming plenty of bugs and even issuing two out-of-band updates to resolve some of the most severe bugs. Speaking of severe bugs, earlier this month, Microsoft acknowledged reports of certain computers not being able to boot after applying the latest security updates and crashing into black screens of death with an "unmountable boot volume" error." Now, Microsoft has more details about the issue.

Fortunately for regular consumers, this issue appears to be limited to commercial PCs. Unfortunately for those using commercial PCs, there is still no easy way to mend affected systems. Microsoft says that the reason the "unmountable boot volume" error appears is the "improper state" that systems end up in after undoing failed December 2025 security updates.

Here is what the company says:

Recent investigations have determined this issue can occur on devices that failed to install the December 2025 security update and were left in an improper state after rolling back the update. Attempting to install Windows updates while in this improper state could result in the device being unable to boot. We are working on a partial resolution that will prevent additional devices from resulting in a no-boot scenario if they try to install an update while in this improper state. However, this partial resolution will not prevent devices from getting into the improper state in the first place, nor will it repair devices that are already unable to boot. We continue to investigate why these devices are failing to install Windows updates or
potentially getting into this improper state.

While this problem is not affecting home users, they have plenty of headaches to deal with on their own. From frozen and broken apps to the inability to shut down their computers or run device-specific software on Microsoft's own handheld, the latest Windows updates give something for everyone, showing the poor state of quality assurance in Microsoft's software labs as the company leans more into AI despite the user pushback.

Source

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Posted Thursday 29 January 2026 at 6:49 am AEST (my time).

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