We had this happen during a long road trip. For some reason, the volume knob stopped working, volume was fixed at 30 without any way to adjust it. Steering volume controls also made no difference. I turned the car off & on hoping to reset the system and as a result we had no sound at all. I suppose volume was stuck at 0, but there was no way to check.
The solution was to remove the two fuses for the radio and amplifier, then replace them. I suppose disconnecting the battery would have worked, but that seemed extreme. After the fuses were re-seated, everything was back to normal.
I hope that helps someone.