My gaming PC worked normally for several hours last night, then was shut down and left untouched. This morning it showed absolutely no signs of power: no fans, debug LEDs, or beeps. I recently replaced the power supply after the previous one failed, so I initially suspected the PSU. Removing the graphics card made no difference, and bypassing the case power switch by shorting the motherboard header pins manually also produced nothing. I removed the modular PSU from the case, disconnected its cables, and used the manufacturer's paperclip test on pins 16 and 17. The PSU fan spun during that test, but it does not spin when the PSU is connected to the motherboard's 24-pin and CPU power connectors. I also tried resetting the CMOS without success. Does this point to a failed motherboard, or are there other checks I should perform first?
2 Answers
A CMOS reset is worth trying: disconnect AC power, remove the CMOS battery for several minutes, then reinstall it and test again. Since that did not help here, the next step is to verify every connection, especially the motherboard's 24-pin connector and the separate CPU EPS connector near the processor. Make sure the CPU cable is an EPS/CPU cable, not a PCIe cable, and do not mix modular cables from different power supplies. The paperclip test only shows that the PSU can start its fan; it does not prove that the PSU is healthy under load. If possible, test with a known-good compatible PSU.
With the GPU removed and the case switch bypassed, try a bare-minimum test outside the case: motherboard, CPU and cooler, one RAM stick, PSU, and the onboard power connections only. Disconnect drives, USB headers, front-panel wiring, and other accessories. This can rule out a short against the case or a faulty peripheral. If there are still no LEDs, fans, or other signs of standby power with a verified PSU, the motherboard becomes the most likely failure, though the PSU should ideally be tested with a proper tester or another known-good unit first.
I already tried removing and reinstalling the CMOS battery, but it made no difference. I’ll recheck the CPU power connection and try another compatible PSU before replacing the motherboard.