I bought this PC secondhand about a month ago. It worked normally after I replaced the RAM, but now pressing the power button produces absolutely no response: no fans, LEDs, sounds, or even a brief twitch.
The system has an Intel i5-10400, MSI MPG Z590 Gaming Plus motherboard, Gigabyte RTX 3080, Corsair RM850 power supply, 16GB of Corsair Vengeance LPX 3600MHz memory, a DeepCool air cooler, and a Fractal Design Define 7 XL case.
So far I've reseated the 24-pin motherboard connector and CPU/EPS connector, cleared the CMOS, discharged the system with the PSU unplugged, shorted the motherboard's power-switch pins directly, removed USB devices, tried booting without the graphics card, tested with one RAM stick, and used another AC power cable. The PSU switch is on. There were no crashes or other warning signs beforehand.
The PC was transported in a car recently, although it worked afterward, and there was a power outage a few weeks ago with no immediate problems. I'm currently suspecting either the RM850 or the motherboard. What other safe checks should I perform before replacing parts?
4 Answers
If you replace the PSU, use every modular cable that comes with the replacement. Don’t reuse the old PSU’s modular cables, even if the connectors appear identical, because the wiring can differ and damage the components.
Start by confirming the basics: test a known-good wall outlet, bypass any power strip or surge protector, check the breaker, and make sure the AC cable is fully seated at both the wall and PSU. Since there isn’t even a fan twitch, the PSU is the first major suspect. A PSU tester, multimeter, or the manufacturer’s paperclip test can help check whether it starts, but be careful and follow the instructions closely.
Try a bare-minimum test outside the case to rule out a short. Put the motherboard on its cardboard box and connect only the CPU, cooler, one RAM stick, 24-pin power, and CPU power. Start it by briefly bridging the power-switch pins. If it starts, reconnect the components one at a time. If it remains completely dead, the likely possibilities are the PSU, motherboard, or CPU, with the PSU being the easiest one to test first.
A multimeter or dedicated PSU tester is useful before buying parts. Check whether the PSU is receiving AC power and whether its outputs are present, rather than relying only on the paperclip test. The paperclip method can show that the PSU starts, but it doesn’t prove that the supply is healthy under load.
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