This is very annoying on a weekend...
Have you tried leaving it unplugging from the mains for several minutes? If not, remove mains plug, disconnect all the speakers and inputs etc. to see if it is a blown speaker or a short circuited cable that is the cause... with only the power supply on and it is still the same, it has obviously developed a fault. :sad:
On my 6004 the master reset is achieved by pressing the menu and enter buttons together. If this still doesn't do the trick, It would appear the overheating protection wasn't quick enough to prevent some kind of damage and repair is necessary.