WD has free software that will try to tell you what's going on in the drive.
If the unit won't power up, check the AC adapter.
If the adapter is OK and if it's the unit that's not powering up, as opposed to the drive, you may be able to pull the drive out and connect it to a cheap'n'cheerful drive case or adapter to confirm whether the drive is actually dead.
While the case is open, see if there are any blown fuses.
I don't know the details of your unit, but AC adapters and external drive cases have both given me way more problems than the hard drives themselves ever have.