Re: Is one of my drives dead?

WD External Drives External Drives for Mac
2

To determine if the drive failed you can try:

  1. Different cable
  2. Different power adapter
  3. Check Disk Utility

Try the steps on the link bellow:

WD external drive is not assigned a drive letter by Windows or Mac OSX and data on the drive is inaccessible

http://wdc.custhelp.com/app/answers/detail/a_id/1164