Write down all fixed Disk and CD/DVD drive letters so as not to delete them.
1. Login with Administrative privileges.
2. Disconnect all USB or FireWire storage devices.
3. Open Registry Editor and navigate to the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
4. Under HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices there will be registry keys with the name that resembles the format of \DosDevice\X: where X can be any alphabet letter which corresponding to your physical system drive letter.
5. Delete all possible USB drives, FireWire drives and external drives which have a drive letter.
DO NOT delete any of the fixed Hard Disk Drives or CD/DVD optical drives registry values.
Exclude \DosDevice\A: which normally reserved for floppy disk drives.
Let us know how you get on.