My Book Essential 2 TB for mac just made the same situation - suddenly it is dead - no light in it - did I loose all info on the device then?
To determine if the drive failed you can try:
- Different cable
- Different power adapter
- 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