This could be a problem with one (or more) of the built in amplifiers, but first check if all the speaker cables are properly twisted and connected to their posts. There shouldn't be any loose cores that can touch the chassis of the receiver, because this causes a short circuit and makes the receiver go into safety mode (at which it shuts off). Also check the interlinks of the affected source to be sure you don't have some kind of signal loss/interruption.
If this doesn't help or obviously isn't the problem, you should have the receiver checked at a repair centre.