The audio system has two fuses, one for the constant/battery (mostly so you can eject CD's while the car is off) and one for accessory. You've got a 20A fuse under the hood labeled RADIO 1 and a 10A fuse in the driver's kick labeled RADIO 2 - check/replace both. If it's an aftermarket deck, check the fuse(s) on the back/on the yellow (and possibly red) wires.