My home-built PC suddenly stopped starting after working normally the night before. When I press the power button, the fans and most lights come on for about half a second and then shut off, although some always-on RGB lighting stays illuminated. The motherboard's diagnostic LEDs usually indicate RAM and occasionally the power supply. I replaced the motherboard, and a technician tested the 32 GB DDR5-6000 G.Skill Flare kit in another system and said it worked. The system has a Ryzen 7 7800X3D, an ASUS TUF B650-Plus WiFi motherboard, an ASUS 5070 graphics card, and a Corsair RM1000X power supply. Could the PSU be failing, or should I also suspect the CPU's memory controller?
3 Answers
The RAM passing a test in another computer makes the sticks less likely to be the problem, but it does not completely rule out the CPU’s integrated memory controller or a memory-training issue. Try booting with one stick at a time in the recommended slot, disconnect the GPU and other peripherals, and clear CMOS first. If it still instantly shuts off with minimal hardware, the PSU or CPU becomes much more suspicious.
Measuring the 12 V, 5 V, and 3.3 V rails with a multimeter is possible, but it can be misleading because the readings may look normal until the PSU is under load. If you do measure them, use a spare peripheral connector and avoid probing the power-supply socket or shorting pins. For this symptom, a proper PSU tester or replacement PSU is the safer and more practical next step.
A failing power supply is still the most likely explanation, especially since the system shuts down almost immediately and the motherboard sometimes reports a PSU fault. The cleanest test is to try a known-good compatible PSU, connecting only the motherboard, CPU power, and graphics card as needed. A PSU tester or a shop’s diagnostic test can also help, but swapping in a known-good unit is more useful than checking voltage with no load.
A different PSU does not need to match every connector from the current setup for a basic test, but it must have the correct motherboard and CPU power leads. Do not mix modular cables between PSU brands or models.