I think I have a short circuit in one of my PC cases (motherboard/RAM/processor replacement in a HP Pavilion case). Whenever I put in the power cord and turn on the switch (not the power button), it automatically boots up and then shuts off after about 2-3 seconds or just won't turn on if I do it repeatedly.
But everything works normally when I move everything into another case. The HP case doesn't use motherboard standoffs so I just use only the hex-head screws and even if I do put in some, the motherboard doesn't line up with the I/O slot and backplate. And even then it still crashes.
Putting in the original mainboard and power supply makes it crash, same with several different other mainboards. But it did work perfectly once before, before I took it out again.
Does it happen to shut off after almost exactly 5 seconds? If so, im betting on a short in the power button switch, if it is stuck into the pressed position then it will trigger the system to boot once the system has power, but boards will generally shut off if the power button is held for 5 seconds. It would explain why it works in different cases and with several motherboards.
Yes, around 3-5 seconds. I don't exactly remember, but it *might've still booted up even when the power switch connector wasn't connected. Not sure about that but I know it definitely auto-booted and then shut off while the PSU switch was on and I put the power button connector into the front panel pins.
The switch itself isn't stuck physically, so it might be something in the wiring of the connector.