Western Digital has an excellent reputation for its hard drives. However, the power adapters can fail.
If you have a digital voltmeter, check the adapter output. My guess is that you will find zero voltage, indicative of a failed power adapter.
If the hard drive is under warranty, you should have no difficulty with replacement. If not under warranty, I recommend purchasing a replacement adapter from Western Digital, rather than a [i]generic[/i] type which may overload and damage the hard drive motor.
Rick/Portland, OR