Assuming it definitely is a hardware issue, PSU dying would be my first guess.
After that, maybe poor seating of a component or dried out thermal paste where the CPU mates with the heat sink, also possibly dust on the CPU or GPU heat sink vanes causing it to get hot, probably worth checking the vents and fans too to make sure they are free of dust and cooling stuff adequately. If it's none of that, I'd try replacing RAM, then GPU, then CPU.
Chock