I built this PC myself, and it had been working normally for about eight months. I left it unused for roughly 50–60 days, and now it will not start. The mouse lights up, so the motherboard seems to be receiving some standby power, but pressing the case power button produces no motherboard response and none of the fans spin. I already tried briefly shorting the power-switch pins on the motherboard, but that made no difference. The system uses an MSI B550M PRO-VDH WiFi motherboard, Corsair RAM, a Gigabyte RTX 3060, and a Cooler Master MWE V3 550 Bronze PSU. There was a recent power outage, although the PC was connected through a UPS. What should I check first?
4 Answers
Since shorting the power-switch pins had the same result, the case button and its cable are probably not the issue. Turn the PSU off and unplug the system, then reseat the 24-pin motherboard cable, the CPU EPS cable near the top of the board, the graphics-card power cable, and the RAM. Also inspect for loose connectors, burn marks, moisture, or damaged plastic.
The CMOS battery is possible, but it usually causes BIOS settings to reset rather than making every fan and light stay completely off. Replacing the CR2032 is inexpensive, but I would check the power cables and PSU first. Disconnect power, remove the battery for a few minutes or use the clear-CMOS procedure in the motherboard manual, then reinstall it and test again.
You can test the PSU separately by following the manufacturer’s jumper-test procedure, with the PSU disconnected from the PC. However, that test only shows whether it starts up and does not fully prove that it is healthy under load. If you are new to PC building, borrowing a known-good PSU or taking the system to a repair shop is safer and more conclusive.
I do not have a spare PSU. Mine is a Cooler Master MWE V3 550 Bronze, so I may need another way to verify it.
A lit mouse only proves that the PSU is providing standby power; it does not prove that the main 12 V outputs are working. The PSU could still have failed, especially after a power event, or another component could be preventing it from starting. Testing with a known-good compatible PSU is the most useful next step if you can borrow one. Do not open the PSU itself.
I already tried bypassing the case power button directly on the motherboard, but there was still no sign of life.