My custom-built computer suddenly stopped starting after working normally the night before. When I press the power button, the fans and most lighting turn on for about half a second and then everything shuts down. The always-on RGB lighting remains illuminated. During that brief startup, the motherboard's RAM warning light comes on, and occasionally the PSU warning light does too. I already replaced the motherboard, and a technician tested the RAM in another system and said both sticks worked. The system uses a Ryzen 7 7800X3D, an ASUS TUF B650-Plus WiFi motherboard, 32 GB of DDR5-6000 G.Skill Flare memory, an ASUS RTX 5070, and a Corsair RM1000X power supply. Could the PSU be failing, or should I be looking at the CPU's memory controller or another component?
2 Answers
You can test the PSU’s 12 V, 5 V, and 3.3 V rails with a multimeter, but measuring only while the PC is idle may miss a fault. The safer and more conclusive option is swapping in a confirmed-working PSU with enough CPU power capacity. If the replacement PSU behaves the same way, test with one DIMM, no GPU if the board supports basic diagnostics, and minimal connected devices. At that point the CPU, socket, or memory compatibility becomes more likely.
A failing power supply is a strong possibility, especially since the system immediately powers off and the board sometimes reports a PSU fault. The fastest way to narrow it down is to test with a known-good compatible PSU, connecting only the motherboard, CPU power, and the minimum hardware needed to reach the diagnostic lights. The graphics card’s dedicated connector is not required for a basic motherboard power test. Also try one RAM stick at a time in the recommended slot, reseat the CPU power cables, and clear the CMOS.
My older PSU may not have the right connector for the graphics card, but I can take the system and PSU in for a known-good power-supply test. I also wondered whether the CPU’s memory controller could be involved because the RAM and CPU-related lights appear during startup.
If you do use a multimeter, be very careful around powered connectors and do not short adjacent pins. A repair shop can perform the rail and load testing more safely.