Was it over heating before this. If so reconnect charger and leave it. The batteries will get kicked back on after some time. But don't try to get a response when you first see the led light turn on. Wait for it to change color shade slightly. If you try to get a response the moment the led turns one. You will get a pink glitch repeat texture screen. This is from extremely lower battery from dead. But after some time you will see the changing battery animation again.
The phone may still work like this but the over heat will drain your battery off or on. It not the CPU or GPU. But like from the daughter board. If the heat is from the lower back on the sim card side.