My KRV-7070 shuts down when it gets too hot. It is either off or on, so your problem is interesting. You didn't mention whether the receiver's built-in fan was working. They can fail, as can the circuitry that turns them on. Also, check that the 8 ohm/4 ohm switch is in the proper position.
Finally, make sure there is adequate ventilation around the receiver. Nothing should be placed on top of it. In fact there should be at least a couple of inches above it, on both sides and behind.