Hi!
So, when you try to turn on the PS3, it's shuts down as in the red light will turn off. And after you press the power button, it will show the red light again, right?
If this is the case, it's something on the motherboard. You need to measure multiple components to check what died on there. It's also very possible that the APU came loose and thus you need to repair that or replace the motherboard.