The usual tests would be (and please tell me if I've missed some, my sub isn't working since it got moved across country)

1. Reseat the adapter.
2. Plug a CD player or MP3 player directly into the sub and see if you get anything (turn it down, first)
3. Hook speaker cables into the high level input from your receiver (again, turn down the sub before you play anything!)

I assume when you say it's got power, it's got a green light on the back?

I am the Doctor, and THIS... is my SPOON!