I would suspect the motherboard. Sounds like there is problem on the motherboard with the power circuitry from the ATX connector.
I have editing some videos and not yet finish. What is the best way to make my PC /hard drive work again. So I can continue do my video editing.
Someone told me. I can replace the motherboard with an identical one. Also, if the CPU is bad, too, replace it. But my PC is 5 years old. It is not easy to get the same model of motherboard and CPU that I used before.
Is there the only way? Reinstall all the software then continue to do what I do before?