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Microsoft investigates Windows 11 boot failures after January updates

Recorded: Jan. 25, 2026, 3 p.m.

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Microsoft investigates Windows 11 boot failures after January updates

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HomeNewsMicrosoftMicrosoft investigates Windows 11 boot failures after January updates

Microsoft investigates Windows 11 boot failures after January updates

By Lawrence Abrams

January 25, 2026
08:20 AM
0

Microsoft is investigating reports that some Windows 11 devices are failing to boot with "UNMOUNTABLE_BOOT_VOLUME" errors after installing the January 2026 Patch Tuesday security updates.
The issue affects Windows 11 version 25H2 and all editions of Windows 11 version 24H2 after installing the KB5074109 cumulative update released as part of this month's updates.
According to Microsoft, some customers have reported that their systems fail to start and display a stop error during boot.

"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," Microsoft stated.
The company says that affected devices will show a black Windows crash screen stating, "Your device ran into a problem and needs a restart. You can restart."
Microsoft says the reported systems are unable to boot into Windows and require manual recovery efforts to boot again.
Only physical devices are reported as impacted by the bug, with no virtual machines reported so far.
Microsoft is asking affected users and administrators to submit feedback via the Feedback Hub app.
Microsoft says it is investigating whether the behavior is linked to a Windows update.
"We are investigating this issue, and we will confirm if this is a regression caused by a Windows update when we have further details. We will update this documentation when more information is confirmed," Microsoft said.
Microsoft also released emergency out-of-band (OOB) updates on Saturday to fix an issue that caused Microsoft Outlook to freeze when PST files are stored in cloud services such as OneDrive or Dropbox.
The company said this issue primarily affects the Outlook class, which is typically used in enterprise environments.

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Related Articles:
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Boot Issues
BSOD
Microsoft
UNMOUNTABLE_BOOT_VOLUME
Windows 11

Lawrence Abrams
Lawrence Abrams is the owner and Editor in Chief of BleepingComputer.com. Lawrence's area of expertise includes Windows, malware removal, and computer forensics. Lawrence Abrams is a co-author of the Winternals Defragmentation, Recovery, and Administration Field Guide and the technical editor for Rootkits for Dummies.

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Microsoft is currently investigating a widespread issue affecting Windows 11 devices following the January 2026 Patch Tuesday security updates. The core of the problem involves devices failing to boot, displaying an “UNMOUNTABLE_BOOT_VOLUME” error and a subsequent “Your device ran into a problem and needs a restart” screen. This behavior is observed across both Windows 11 version 25H2 and 24H2 after installing the KB5074109 cumulative update released on January 13, 2026. Initial reports indicate the issue predominantly impacts physical devices, with no confirmed cases on virtual machines.

The company received a limited number of initial reports detailing the boot failure. The symptoms include a complete inability to initiate the Windows operating system, necessitating manual recovery procedures to regain functionality. Microsoft is actively soliciting feedback through the Feedback Hub app, seeking to pinpoint the root cause and determine if the issue represents a regression introduced by the update itself.

Currently, Microsoft’s investigation centers on determining a connection between the update and the observed boot failures. This investigation is ongoing, with Microsoft stating they will provide further confirmation if the issue is indeed a regression. The company’s response highlights the importance of rapid issue identification and resolution within the Windows update cycle.

In addition to the boot issue, Microsoft had previously released an out-of-band (OOB) update to address a separate problem causing Microsoft Outlook freezes when PST files were stored on cloud services such as OneDrive or Dropbox. This issue specifically impacted the Outlook class, common in enterprise environments.

The situation is being carefully monitored, and Microsoft is urging users and administrators to submit detailed feedback through the Feedback Hub, which will aid in the diagnostic process. As of the date of this report, the precise cause remains unclear, and Microsoft’s investigation is proceeding to establish conclusively whether the January 2026 security update is the source of the problem – or another contributing factor. The company’s commitment to providing updates and guidance as information becomes available suggests a proactive approach to addressing the emergent situation and mitigating potential disruption for Windows 11 users.