My RTX 4090 first started showing artifacts and then stopped producing any video output. The motherboard displayed its red VGA diagnostic light, so I assumed the graphics card had failed. After leaving the PC unplugged for about two months, I replaced the 4090 with an RTX 5080, but I still couldn't get an image. The new card no longer triggers the red VGA light, yet the system still doesn't display anything. I reseated the GPU and RAM, checked all GPU power connectors, tried different display cables, and reconnected the CPU power cables. The PSU was tested in a workshop with another system and was confirmed to work, and the 4090 was also tested there and found to be dead. My CPU is a Ryzen 7 5800X3D, so it doesn't have integrated graphics for testing. Could the motherboard be faulty, or is there anything else I should check?
3 Answers
Since the 5080 doesn’t trigger the VGA warning, the motherboard may be getting past GPU detection but failing elsewhere during POST. Because the 5800X3D has no integrated graphics, you can’t use onboard video to narrow it down. Try a minimal-boot setup with only the CPU, one RAM stick, the GPU, and the necessary power connections. Also clear the CMOS and check whether the board has any other diagnostic LEDs or beep codes.
A PSU starting up or passing a basic check doesn’t always prove it can deliver stable power under load, but testing it in another working PC is much more meaningful. Since both the PSU and the 4090 were tested at a workshop, the motherboard becomes the main suspect. Still, test with a fully known-good PSU if possible, clear the CMOS, and inspect the CPU socket and motherboard for damage.
The fix turned out to be the motherboard’s CMOS battery. Replacing the battery restored video output. If the system has been unplugged for a long time, a weak battery can sometimes cause BIOS settings or POST behavior to become problematic, so it’s worth trying a fresh CR2032 battery along with a CMOS reset.
I couldn’t test integrated graphics because the 5800X3D doesn’t include an iGPU. The old card was also tested separately and confirmed dead.