WD passport ext drive

If you are getting a driver error in the system tray, it may just be that you need to install the WD SES driver.
Choose WD SES Driver Setup (x86) or WD SES Driver Setup (x64) as appropriate: http://wdc.custhelp.com/app/answers/detail/a_id/5419/session/L2F2LzEvdGltZS8xMzgxODcwNjAyL3NpZC94ckEzSlRDbA%3D%3D

If that is not the issue, the drive may just need a letter manually assigning it, so look in Disk Management to see if the drive is shown there without a letter. If it is, right-click it and choose "Change Drive Letter & Paths", then click "Add".
Choose a letter or accept the default. Click 'OK' and wait a few seconds.