Microsoft Acknowledges BSOD and Boot Problems in Windows 11 KB5074109 January Update for Some PCs

The January 2026 Update for Windows 11, specifically KB5074109, is leading to significant malfunctions for certain users. Microsoft has recently updated its support documentation, acknowledging that while the majority of home users are not affected, some commercial PCs are experiencing critical boot issues.

On January 23, Microsoft confirmed the existence of reports indicating that certain PC models were unable to restart, though they initially refrained from directly linking these failures to the recent update. As of now, the company has verified that a small segment of systems is indeed encountering boot failures post-update and has classified this as a recognized issue that is under active review.

The problematic update impacts devices operating on Windows 11 builds 25H2 (26200.7623) and 24H2 (26100.7623).

Users facing issues may encounter a Black Screen of Death (BSOD), which has recently been redesigned to fit the aesthetic of Windows 11. Notably, the traditional blue screen has been replaced, aligning with the updated user interface.

The BSOD manifests as an UNMOUNTABLE_BOOT_VOLUME error, preventing the system from booting without human intervention. Affected users must access the Windows Recovery Environment (WinRE) to initiate recovery procedures.

Microsoft has attributed these issues primarily to a Windows Update complication, specifically impacting certain commercial systems rather than consumer devices. This indicates that the updates interact adversely with existing system states rather than external factors such as drivers or third-party applications.

Understanding the Boot Failure Issues

Microsoft clarified that instances of the UNMOUNTABLE_BOOT_VOLUME error predominantly affect machines that encountered difficulties with the installation of the December 2025 security update. When these updates were rolled back, the systems were left in an “improper state, ”yet continued to function until the installation of KB5074109 triggered the issue.

Typically, Windows updates are designed to be executed on devices in a stable state. However, due to the pre-existing irregularities on these affected machines, the installation process for the January 2026 update interacted with low-level system components, leading to degradation in system functionality.

This degradation culminates in the error code 0xED, rendering the systems incapable of booting without user intervention.

In recent findings, Microsoft stated: “This issue can manifest on devices that experienced failures during the December 2025 security update installation and were subsequently left in an improper state. Attempting further updates under these conditions can result in boot failures.”

The company is currently implementing partial solutions to preclude additional devices from succumbing to similar boot failures; however, this will not remediate devices already affected.

Additional Challenges in the January 2026 Update

Aside from the critical boot issues, the January update has introduced several additional concerns, including problems with Outlook, unresponsiveness in third-party applications, and issues with sleep mode on older machines. Other minor complications include failures in Remote Desktop and shutdown functions.

In response, Microsoft has already released an out-of-band update (KB5078127) aimed at rectifying Outlook-related issues and is actively investigating other reported problems.

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