Quote:Microsoft has officially acknowledged a critical bug affecting Windows 11 users on certain Samsung devices, in which the system drive (C: becomes completely inaccessible after installing the February 2026 security update. The company is now actively investigating the issue in coordination with Samsung.

After installing the February 2026 Patch Tuesday update (KB5077181, OS Build 26100.7840), affected Samsung devices display the error message: “C:\ is not accessible – Access denied.”

The error effectively locks users out of their own system drive, blocking the launch of applications, including Microsoft Outlook, Office apps, web browsers, system utilities, and Quick Assist.

The failure is not triggered by any specialized operation. Routine tasks such as opening files, launching applications, or performing standard administrative actions are enough to surface the error.