I've suggested this before but it's worth repeating. A modern receiver/processor is very much like a computer. If you've had it for a long time it probably is full of dust. If your sub regularly shakes the room some of the circuit boards may have come partially out of their sockets. If you live in a place with high humidity connectors may have built up oxides or started to corrode. All of these environmental conditions can cause significant problems or apparent failure.

It probably is worth taking off the cover, using canned air or a vaccuum (be careful not to let the pipe touch anything in the component) to blow out all the crud, and reseating the circuit boards.