I built this PC myself and it had been working normally for about eight months. I then left it unused for roughly 50–60 days. Today, it would not start at all: pressing the case power button does nothing, the fans do not spin, and there are no motherboard indicator lights. The mouse does light up, so the system appears to be receiving some standby power. I already tried shorting the power-switch pins directly on the motherboard, but that made no difference. The system uses an MSI B550M PRO-VDH WiFi motherboard, a Cooler Master MWE V3 550 Bronze PSU, Corsair memory, and a Gigabyte RTX 3060. There was also a recent power outage, although the PC was connected through a UPS. What should I check next?
3 Answers
Since shorting the motherboard’s power-switch pins also did nothing, the case button and its cable are probably not the problem. Turn the PSU off and unplug the PC, then reseat the 24-pin motherboard cable, the CPU power cable near the top of the board, and the GPU power cable. Also inspect for burn marks, corrosion, loose parts, or anything that may have come loose while the system was sitting unused.
Replacing the CMOS battery is worth trying if the BIOS settings are lost, but a dead CR2032 battery usually does not prevent the fans and power circuitry from starting completely. It is less likely than a loose connection, PSU failure, motherboard fault, or a short. After checking the cables, try a minimal setup outside or inside the case: motherboard, CPU and cooler, one RAM stick, and PSU only. Disconnect the drives, front-panel USB devices, and graphics card if the CPU has integrated graphics, then see whether the board shows any diagnostic activity.
A battery replacement may help with reset settings, but it probably won’t explain why there are no fans or motherboard indicators. I’d check the PSU and power connections first.
The mouse lighting only proves that the PSU is providing a small amount of standby power. It does not prove that the PSU can deliver the 12-volt power needed to start the system. A failed PSU, a damaged motherboard, or another shorted component could all cause this symptom. If possible, test with a known-good PSU from another PC. You can also perform a proper PSU jumper test according to the manufacturer’s instructions, but disconnect the PSU from all components first and be careful—passing that test still does not guarantee the PSU is healthy under load.
I don’t have a spare PSU, so I may need to take the system somewhere for testing. The power outage could have damaged something even though the PC was connected to a UPS.
I already tried starting it directly from the motherboard pins, but I’ll disconnect and reseat the main power cables and inspect the board carefully.