TECH NEWS – It is not recommended to download the latest update until the Redmond-based tech giant fixes the new bug.

If you downloaded the KB5074109 Windows update and now your computer won’t boot, know that you’re not alone. In a support document, Microsoft informed users that it is investigating reports of startup errors on devices after the January 2026 update and subsequent updates. This document is only accessible to Microsoft 365 business accounts, suggesting that the startup issue primarily affects business devices. However, it has not yet been confirmed which devices are affected by the problem.

“Microsoft has received reports of devices failing to boot with stop code “UNMOUNTABLE_BOOT_VOLUME” after installing the January 2026 Windows security update (KB5074109), released on January 13, 2026, and subsequent 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,” the document says.

Comment
byu/Dry-Recognition-5413 from discussion
inDell

This error code typically indicates a problem with the boot driver, but it can also be caused by corrupted files or a memory problem. However, this is not the first time that users have blamed Windows updates for this error code. On January 24, an unexpected update was released that resolved the issue of applications not responding when saving files to the cloud. Microsoft has only received a limited number of reports, so it is unclear how widespread this issue is. Microsoft has made it clear that this issue currently only occurs on physical devices and has not been detected on virtual machines. The issue appears to affect only Windows versions 26200.7623 and 26100.7623 or later, and it is being investigated.

To check if you are affected, go to Settings > About > Windows Information and check the operating system version. If you have installed it and encountered this problem, you will need to use the Windows recovery option. In the worst case, you will need to reinstall the operating system completely.

Source: PCGamer, Windows Latest, Microsoft, Microsoft Docs