Hello,
Take a look at these links. Hope they can help with your issue.
WD external drive is not assigned a drive letter by Windows and data on the drive is inaccessible
How to change the drive letter assignment in Windows 8, 7, Vista, XP or 2000
Hello,
Take a look at these links. Hope they can help with your issue.
WD external drive is not assigned a drive letter by Windows and data on the drive is inaccessible
How to change the drive letter assignment in Windows 8, 7, Vista, XP or 2000