depending on who installed it, they might have tagged 12V/ACC/ground behind the radio...if so, never go there again because theyre a bunch of ****in retards...but its possible.
You didnt have to disconnect the battery or anything did you? Check under your dash, you should see some random fuses hanging around, pull them...one at a time and check to see if theyre blown. Dont have more than one fuse pulled at once though. In theory, it shouldnt matter...but a theory is just that...a theory