Why does the system unit not respond to "power on"?

Question

Power Supply

Hello! I have such a question .. The system unit stood on my cabinet for a month, then I decided to turn it on. I press the button - zero reaction. Not a sound. The fan is not spinning. I tried to test the PSU by shorting green and black. The hard drive connected to the PSU starts spinning. As soon as I connect the PSU to the motherboard - I press the button - It does not turn on, and the fans do not work. I decided to close the power pins on the motherboard (POWER SW) - Zero sense. What could be the problem? Naturally - at least in something .. I think - maybe the motherboard of that ...
By the way, such an effect was observed before - when the system unit was turned on - it sometimes turned on for the tenth time the button was pressed. Such things .. Can anyone help with advice? I don't want to take it to service..

Answer 1

Maybe the PSU, maybe the board, maybe something else. First you need to try a known-good PSU.

Answer 2

Pull everything out of the case, disconnect everything from the motherboard, check and if necessary replace the bios battery, connect the motherboard to a working PSU, connect some kind of cooler to the board and a speaker. Briefly close the Power SW.
If the board starts up, then it should swear at the lack of CPU / RAM / Video / etc, and earn a cooler. It happens that the board is sad without a CPU, plug it in, the cooler is nearby, check if the CPU heats up when turned
on. Is there a standby power indicator and is it on?