Panasonic receiver shuts down

I have a Panasonic sa-he200 receiver that has worked fine for a couple of years, but is now acting up. It overloads and shuts down after a short period of time. I noticed that the fan does not come on until after it shuts down.Shouldn't it run all the time to keep it cool ? It does this even when it's not in an enclosed cabinet.Do you know of an easy fix ?