Overview
- Microsoft says KB5074109 can cause black-screen no-boot errors on a limited set of commercial Windows 11 PCs.
- The issue affects systems on Windows 11 25H2 Build 26200.7623 and 24H2 Build 26100.7623 after installing the January cumulative update.
- A partial mitigation now blocks additional devices in this improper state from entering the no-boot condition, but it does not repair machines already unable to start or prevent the state from occurring.
- Impacted devices show an UNMOUNTABLE_BOOT_VOLUME error and require manual recovery using the Windows Recovery Environment.
- Microsoft says the problem currently involves physical commercial devices rather than consumer PCs or virtual machines, and the investigation continues.