My PC suddenly stopped displaying video after being left running. The system stayed powered on, but the monitor received no signal. I tried different HDMI cables, replaced the power supply, cleared the CMOS, and completely rebuilt the system.
My system uses a Ryzen 7 5700X, an MSI B550-A Pro motherboard, an RTX 3060, four 8GB Corsair DDR4 modules, and a Corsair RM650e 650W PSU. The 5700X has no integrated graphics, so video testing requires a discrete GPU.
I tested my husband's known-working RTX 4080 in my PC, but it also produced no display. With that card installed, my motherboard's CPU debug LED came on rather than the VGA LED. I also tested my RTX 3060 in his PC, where it produced no display and triggered the VGA debug LED. This makes me unsure whether the 3060 itself is faulty, whether my motherboard or CPU is failing, or whether more than one component was damaged.
The RAM behavior has also been inconsistent. With two memory sticks installed, the keyboard and mouse did not light up, while all four sticks made them light up. On one occasion, the system displayed video and booted into Windows, but it lost display again after roughly four or five minutes. After clearing the CMOS, I briefly saw the CMOS-reset message while using the 4080, but I have not been able to reproduce it.
Since the PSU has already been replaced with new cables and the system has been rebuilt, what should I test next? Is there a reliable way to isolate the faulty component before replacing the GPU, motherboard, CPU, or RAM at random?
2 Answers
The motherboard is the strongest suspect, although a failing CPU or memory subsystem could also cause a CPU debug light and inconsistent POST behavior. The debug LED identifies where startup stopped, not necessarily the part that failed. Test with the board outside the case using only the CPU, CPU cooler, one known-good RAM stick in the recommended slot, the 4080, and the necessary power connections. Disconnect storage, USB devices, and other extras. Try each memory stick individually and inspect the CPU socket and motherboard for bent pins or damage. If the system still cannot POST with known-good parts, the motherboard is probably the part to replace or RMA first.
Clear the CMOS whenever changing hardware, then give the board time to retrain the memory. Use the jumper or remove power and the battery according to the motherboard manual, then install one RAM stick in the recommended slot. Do not rely too heavily on the CPU or VGA LEDs; a failed memory initialization or unstable board can leave different LEDs lit depending on how far POST gets. Also make sure the monitor is connected to the graphics card, not the motherboard video outputs, because the Ryzen 7 5700X has no integrated graphics.
I cleared the CMOS before testing both cards. I did briefly see the reset message with the 4080, but the result was not repeatable afterward.
The motherboard is my leading suspicion too. I was mainly worried because my 3060 also failed in the other PC, which makes me wonder whether the card and motherboard were damaged at the same time.