Tv will go black sound will last a few seconds. It

If the set shuts down and cycles 3 times before the set goes to the 3 flashing lights on front, I would suspect the lamp causing this issue. Each time the set restarts on its own it boosts the voltage to fire the lamp and after 3 times it's basically 3 strikes and you're out. If you haven't replaced the lamp in a long time then suspect that first.