homelab
System as it was originally, and with the Optical Drive removed along with the big metal bay that it sits in. No SATA data or poeer is plugged in. I reseated the battery and the power button cable.
Edit: installed the cage again as it has structural purpose.
PSU light turns green for a few seconds, goes blank. Power button at the front has no reponse at all when I press it.
If that passes, it's the power button (unlikely, it's just a button) or the motherboard or some component. If the power button contacts are exposed, and assuming it's a regular momentary contact switch, you should be able to bridge them to complete the power button circuit, eliminating the button itself.
It is a buttonless. So I plug in the cord, and the PSU will light up green for ~3 seconds and then turn off. It does not light up again. Does this mean it passed or failed the test?
No idea. Continue to the next bit.