recently bought a 760. previous owner had aftermarket radio, original radio was reinstalled when i bought it. drove the car until radio display light came on, had the code ready, entered it and the radio worked fine (except the only speakers working are in the dash} took car to volvo guru for him to bless my purchase. he looked it over and after all important issues were addressed i pulled radio out, we looked it over slid it back in and i drove away. PROBLEM now the radio works for about 30 seconds and shuts off. radio will not work again until after the car is shut off, then it works for another 30 seconds and stops. anybody have any suggestions as how to remedy this?