Single Status Update
Sorry for tech support, but I figured there are several regulars here who would immediately know what to tell me...
I was installing windows on this new PC, which I was switching on for the first time. It was working fine for about 10 minutes into the installation and then it suddenly it shut off and tried to restart. It got as far as the little PC speaker beep, but about a half-second later it "clicked" off. Since then this failed start just loops over and over again until I switch off the PSU (pushing or holding the panel power button does nothing). All the fans (and the VPU light) turn on for the half-second, but no signal is sent to the monitor and there are no noises other than the fans.
Then I unplugged everything except the mobo (and with it the processor of course) and case fans, and now it does the same thing except it lasts 3 seconds each time instead of one.
So since it runs a bit longer with less things to be powered, is it safe to assume it's the PSU?
Unfortunately I can't check the PSU with another comp because I don't have anything else with a 24-pin power plug, and vice versa checking the new comp with the an older PSU.
Hm... After letting it sit for a while it did the same thing on a 10-or-so second loop.
And THEN earth control pinpoints... wait, I mean, and THEN I got the advice to try running it on a piece of cardboard, which made it suddenly work. Seems odd since it was inconsistent depending on plugged-in devices before, but maybe it's a short or something? I'm leaving it on for now to see what the temp does.