First, check the fuse panel to see if fuse is burned out. If fuse is OK, might have to pull radio chasis out of dashboard to check connections. Could be corroded copper wire in radio harness (hope not - that can be a pain to fix). I f radio is original it's 12 yeads old - if aftermarket radio, could be cheap to begin with and just broken inside. All electrcal problems are a matter of elimination - you check one thing at a time. If a light won't go on in a lamp in your house, you check the bulb. If bulb good, check plug. If plug OK. Check switch. Same with a car.
Or check the fuse in the back of the stereo they usually have a 10 amp fuse in the aftermarket