My 595 did the same thing once when I was showing off the unit with the opening battle of "Gladiator". Did yours come on after cooling? Try unplugging the unit for 15 minutes and trying again. Check for lose spaeaker wire strands (I have since gone to using banana plugs).
If that does not work I have heard that some Receivers have internal breakers that need to be reset at the service centers. So you may have to send it out.