Electrical 1992 GT - battery / stereo problem

How old is the battery? They can go bad anytime but surely after a few years, especially if the car doesn't get driven that much. Charge the battery fully then do a load test on it. Many local parts stores will do a load test for free. You can pull the battery and take it there.

For the radio not working, have you checked the fuses?

John Dirks Jr is right about the battery... They never last as long as we think they should, and about your radio fuses. One thing to remember... The radio has two circuits to run. Constant 12v for the memory, and switched 12v from the ignition. Both have to work in order for the radio to turn on. Check fuse 8 and 11.

Other times, if the voltage goes below 8.5vdc, the radio may have gone into protect mode. You may have to simply unplug the radio fuses both together and it may fix it. The other option, is to check the fuse on the very back of the radio head unit. The exact location varies by make/model, but its usually right next to the wiring harness. If you don't immediately see it, pull the harness from the radio. Sometimes they are hidden under a piece of plastic on the harness itself. That little mini fuse could have blown as well. They are usually red/10A so they don't hold up to much. Just a thought.