on car seats in the cooler weather i have coated the leather, placed a garbage bag over the seats and then wrapped to seats in hot damp towels. it has worked well in the past for me. not sure if thats the recommended process.
factory amp? check the fuses.
perhaps it had an aftermarket system and the prior owner replaced with the factory and did not hook it up
if it turns out to be a bad radio, i have one from my wifes old minivan in the garage you can have for shipping costs.
if it is concrete, SAKRETE makes a concrete disolver that may work to help removing it. i have used it before on a metal house door after having concrete slashed on it, and it did no damage to the paint.