The computer in the payment terminal does not turn on, is it the power supply?

Question

Iron

Suddenly, the payment terminal was completely disconnected. I was not at that moment next to him, I did not see what happened. A receipt printer and a computer are connected in it through the UBP. The printer's power supply is working properly, but the computer's power supply is not working. I disconnected everything from the power supply and closed the contacts (green and black) with a paper clip - the unit worked. I left the power supply of the motherboard and the processor - it worked. I connect the hard drive and other expansion boards - the unit does not turn on. When you try to connect something other than the motherboard and processor to a hot one, the unit turns off instantly. I tried to connect a second power supply for verification - the story repeats with it and with the third block. What could be the problem? All power supplies are no more than 500W, before that everything worked properly, the terminal worked for days.

Answer 1

is it the power supply?

No. Because it works separately.

I connect the hard drive and other expansion cards

Connect in turn, before connecting, unplug the computer from the outlet.