Microsoft Investigates Boot Failure Issues Following January Update

If you experienced boot problems after installing the KB5074109 Windows update from January, you’re not alone in facing this issue.

According to a recent update from Microsoft, the company is looking into reports from users regarding devices that fail to boot after applying the January 2026 update and subsequent updates.

This information is contained in a support document that’s only available to Microsoft 365 business users, suggesting that the boot failure issue primarily affects business-oriented devices. However, Microsoft has yet to provide clarity on which specific devices are impacted.

The support document reveals, “Microsoft has received a limited number of reports concerning devices that fail to boot, displaying the stop code ‘UNMOUNTABLE_BOOT_VOLUME’ following the installation of the January 2026 Windows security update (KB5074109), which was released on January 13, 2026, and later updates. Affected devices exhibit a black screen accompanied by the message ‘Your device ran into a problem and needs a restart. You can restart.’ At this point, the device cannot fully start up and requires manual recovery actions.”

Typically, this particular error code indicates an issue with the boot drive, although it may also stem from corrupted files or even memory-related problems. Notably, this isn’t the first instance where users have linked a Windows update to this specific error code.

In addition to the boot failure issue, there have been other complications arising from the updates released this month. A surprise update on January 24 addressed a problem where applications became unresponsive when attempting to save files to the cloud.

Microsoft has only noted a ‘limited’ number of incidents, leaving the extent of the problem unclear. The company further specifies that this issue currently affects only physical devices and has not been detected on virtual machines. This issue appears to affect users running Windows builds 26200.7623 and 26100.7623 or newer.

To determine if your PC might be impacted, navigate to ‘Settings’, select ‘About’, and scroll down to ‘Windows info’. The ‘OS build’ section will indicate your current build. If you haven’t yet installed the KB5074109 Windows update, it would be wise to wait until Microsoft resolves this issue.

For those who have already updated and are experiencing difficulties, you may need to utilize the Windows Recovery option or, in the worst-case scenario, perform a clean reinstall of the operating system. While reinstalling Windows can be a frustrating experience, options for casual users are somewhat limited. Some users are contemplating alternative operating systems, with Linux being a popular consideration among those looking for a change.