They'll have a spare PSU to swap in as a test. Yes you can buy a Volt Meter and PSU tester but that's as much as a new PSU.
I understand you don't want to randomly buy parts but is it worth investing in the test gear?
I'm not there to work this but the usual is found with google like this: "The Dead PC."
You pull it out on cardboard and start with just two parts and work your way up.
I have used older custom built pc for over a year now without any problems. Then suddenly it refuses to start. Pressing power button does nothing, no beeb, fans don't start to spin, it is cold dead. I know a little bit about PCs but not nearly enough to fix this. This is what ive done so far:
Unplugged all cables from psu, 24moba, 4pin pcu, 2x6 pci to gpc and the hdd cord. Tried to plug them in one by one.
The led on Motherboard and led on graphic card are working when psu is switched on.
Removed ram and tried using only 1 ram,changing its place.
I removed the psu and put metal clip to green pin and the closest black and plugged it to power and the psu fan started to spin.
The last pc shutdown was normal and pc has never shown any symptoms of slowing down or any malfunctioning. What are my next steps so I can narrow down the problem or even fix it? I dont want to randomly buy new parts and I really hope the problem wont be in motherboard.

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