My PC shut off suddenly while I was gaming. The case fans continued spinning, but there was no display, no POST, and holding the power button would not shut it down. After unplugging the system, holding the power button for about 10 seconds, and reconnecting it, the fans spun again but nothing else worked—not even my USB devices.
The system uses a Ryzen 7 9800X3D, ASUS RTX 4080 Super ProArt, ASRock B650 Lightning WiFi motherboard, 32GB of TeamGroup DDR5 memory, and a Cooler Master 850W SFX power supply. I removed the graphics card and connected HDMI directly to the motherboard, tested both memory sticks individually in different slots, cleared CMOS, and reduced the system to the motherboard, CPU, PSU, and one RAM stick. The result is always the same: fans spin, but there is no POST or other sign of life, and the system can only be stopped by unplugging it.
The GPU power connector looks normal, so I do not see obvious signs of a damaged cable. At this point, I am trying to determine whether the motherboard, power supply, or CPU is most likely at fault. What would be the best next diagnostic step, and which component should I suspect first?
4 Answers
Try the stripped-down setup with a known-good power supply, preferably one with the correct EPS and motherboard cables. A failing PSU can still spin fans while failing to provide stable power for USB initialization or POST. Do not mix modular cables between power supplies.
Consider whether there was a power disturbance at the time of the failure. Voltage dips or surges can damage a PSU and sometimes take the motherboard or other components with it. If possible, test with a different known-good PSU and use a quality surge protector or battery backup afterward. The CPU is usually less commonly the failed part, but an abnormal voltage event or motherboard voltage problem can still damage it.
A failed motherboard is a strong possibility, especially if the system suddenly died and now only powers the fans. The quickest way to separate the board from the CPU is to test the processor in another compatible B650 board, or install a known-good compatible CPU in this board. Borrowing a board or buying an inexpensive used one may be cheaper than replacing parts blindly.
The first thing to establish is whether the board shows any diagnostic LEDs or codes when you press the power button. If there is no POST at all, the motherboard or power supply are more likely starting points than the CPU, although the CPU cannot be ruled out yet.
I cannot get into the BIOS or reach POST. I have not noticed any diagnostic LEDs on this small-form-factor board, though I will check the manual again.
Contact the board manufacturer first, but a cheap compatible replacement board can also be useful for testing. If the PSU caused the failure, it is possible other components were affected, so test carefully rather than assuming the CPU is safe.