I recently set up a refurbished gaming PC for my girlfriend after she moved. It has a Lian Li case, Intel i5-12400F, Gigabyte RTX 3060 Ti, 48 GB of DDR4 memory, a 1 TB Samsung Gen4 SSD, and an FSP Hydro Pro 800W power supply. The day after I finished assembling it, she tried to reorganize the cables even though she has very little experience with computer hardware. She unplugged everything, then connected a USB-A-to-USB-A cable to the USB outlet on a wall socket and the motherboard. After realizing something was wrong, she panicked and unplugged the power supply, which caused a spark. The computer no longer powers on, although there is no obvious burnt smell. What is the safest way to determine whether the power supply, motherboard, or other components were damaged, and what should I test or replace first?
3 Answers
The likely failures are the PSU, motherboard USB circuitry, or both, but the SSD, memory, and graphics card may still be fine. A technician can test each component with known-good equipment and may be able to confirm which parts survived. Since the system was recently assembled, also check whether the PSU or motherboard is still covered by warranty. Do not open the PSU, and discard or clearly label the USB-A-to-USB-A cable unless a specific device requires it.
Stop trying to power it on for now, especially if the cable was connected directly to mains rather than a USB charging port. Disconnect the PC from the wall and inspect the motherboard, USB ports, power connectors, and PSU for scorch marks or melted plastic. If mains voltage reached a motherboard USB port, the motherboard and possibly the PSU may be damaged. This is a good point to have a repair shop test it rather than repeatedly swapping parts or opening the PSU itself.
Begin with the power supply, but do not use the paperclip test as proof that it is safe or fully functional. Test with a known-good, compatible PSU, and make sure every modular cable belongs to that exact PSU—modular cables are not interchangeable. If the replacement PSU still gives no response, test the motherboard outside the case with only the CPU, cooler, one RAM stick, and graphics card if needed. Reseat the 24-pin motherboard cable, CPU power cable, RAM, and front-panel power connector. Do not reconnect the suspicious USB cable.
Removing and reinstalling the motherboard battery is unlikely to repair electrical damage; it only resets BIOS settings. It can be tried later, but the PSU and motherboard should be isolated first.
If the wall socket only had a normal USB charging port, that is very different from connecting the cable to the actual AC outlet. Either way, the spark when the PSU was unplugged means it should be treated cautiously until the PSU is tested.