So my friend Harold has an automotive shop and his diagnostic PC is having persistent, but intermittent problems. Shutting down for no reason, especially when the table it's on gets bumped. It reboots and sometimes never comes back.
He brought it to me and last night I worked on it. Got it to boot up once, then as a test i knocked the case a little. It immediately shut down and started to reboot.
But it never came back.
I worked on it until 1:30 in the morning, removing wires, checking connections, trying to identify the problem and bring the system down to it's least common denominator. In the end, I had everything unplugged except the power supply to the board and I had the CPU and it's fan still installed, and the RAM. This is the minimum configuration, and I should have at least been able to get to the BIOS. No good. It still won't come to life.
So then I took one step further: I removed the board from the case itself, thinking the board was getting shorted out somehow. I put it on a magazine to keep it from sitting on the metal case. Still no good.
I'm running out of tricks. Today I'm looking at it by hooking it up to a different power supply to see if that's the problem.
This thing is a pain in my ass.