Dont forget the fuse box in the engine bay too, might be something amiss there. Id also replace (if you can) the fuses that are marked for the radio just to be sure. Do the usual checks for grounds, proper cable connection between the amp and headunit, as well as to the battery.
Does the rest of the electronics in the car work? Try your lights, indicator, as well as try to start the engine. If they all work, it has to be a fuse or wiring problem to the audio gear. Run over it again and check it to make sure, let us know how it goes :2thumbs: