Are you using registry editor or group policy editor to hide drives in your Computer just try free application NoDrives Manager which allows to hide logical drives, removal drives and CD/DVD drives with few clicks .
All you need to select the drive letters you want to hide from Windows Explorer from NoDrives Manager program window and click Save changes, log off and log on again or restart explorer.
Though these drives are hidden by the NoDrives Manager but can accessible through run command by entering the drive letters.To show the hidden drives again in My Computer just uncheck the drive letter from program Window and restart your Computer for drives to reappear again in Windows Explorer.
NoDrives Manager is freeware.NoDrives Manager works with all versions of Windows .I tested this in Windows 7 and it worked like a charm.