make sure the drive letter is not being used by anything else on your PC.
can check this in disk management and also change the drive letter if needed
go to start, right click on computer and then go to manage
on the next screen on the left hand side go to disk management, on the right you will see the drives, if you need to change the drive letter of the WD right click on it and go to change drive letter, pick a letter not in use and should be fine after that