Helped friend with secure boot, drive letter lost.

Troubleshooting Lost Drive Letter After Enabling Secure Boot: A Guide for Windows Users

Enabling Secure Boot can enhance your system’s security by preventing unauthorized operating systems from loading during startup. However, tweaking your system settings—such as converting a drive to GPT and enabling Secure Boot—can sometimes lead to unforeseen issues. One common problem is the sudden disappearance of drive letters, rendering a drive inaccessible until the issue is resolved.

Recently, I assisted a friend in enabling Secure Boot to participate in the Battlefield 6 beta. During this process, the system’s boot drive was converted from MBR to GPT, and Secure Boot was activated. While the upgrade overall went smoothly, an unexpected issue emerged post-configuration: the NVMe drive used to store the page file lost its drive letter.

The Issue

The NVMe drive, which continued to be formatted with MBR despite the boot drive’s conversion to GPT, became inaccessible in Windows. In Disk Management, the drive appeared greyed out, indicating it was recognized but not assigned a drive letter. When attempting to assign a new drive letter via Disk Management or Command Prompt using DiskPart, Windows responded with an error:

“Assigning or removing drive letters on the current boot or pagefile volume is not allowed.”

This error prevents manual assignment of drive letters on drives that are active system or pagefile volumes, or when certain system protections are in place.

Key Details

The drive in question is an NVMe SSD.
The drive contains the pagefile and has lost its drive letter.
The drive remains MBR formatted, despite the boot drive being converted to GPT.
The drive is recognized by Windows but appears inaccessible due to the missing drive letter.

Troubleshooting Steps and Considerations

Verify Drive Status in Disk Management

Open Disk Management (diskmgmt.msc) to inspect the drive’s status. If it is marked as ‘System’, ‘Boot’, or ‘Page File’, Windows restricts the assignment or removal of drive letters to prevent system instability.

Check for System Volume Restrictions

Windows generally restricts modifying volumes that are actively used for system boot, pagefile, or system protection. You cannot assign or remove drive letters on such volumes while Windows is running from them.