How to restore the system/boot drive letter in Windows
Create a restore point before proceeding with the following troubleshooting steps.
- Make a full system backup of the computer and system state.
- Log on as an Administrator.
- Start Regedt32.exe.
- Go to the following registry key:
- Click MountedDevices.
- On the Security menu, click Permissions.
- Verify that Administrators have full control. Change this back when you are finished with these steps.
- Quit Regedt32.exe, and then start Regedit.exe.
- Locate the following registry key:
- Find the drive letter you want to change to (new). Look for “\DosDevices\C:”.
- Right-click \DosDevices\C:, and then click Rename.
Note You must use Regedit instead of Regedt32 to rename this registry key.
- Rename it to an unused drive letter “\DosDevices\Z:”.
This frees up drive letter C.
- Find the drive letter you want changed. Look for “\DosDevices\D:”.
- Right-click \DosDevices\D:, and then click Rename.
- Rename it to the appropriate (new) drive letter “\DosDevices\C:”.
- Click the value for \DosDevices\Z:, click Rename, and then name it back to “\DosDevices\D:”.
- Quit Regedit, and then start Regedt32.
- Change the permissions back to the previous setting for Administrators (this should probably be Read Only).
- Restart the computer.
For further reference check Microsoft knowledge base article : 223188