I replaced my EVGA RTX 3080 with a Zotac RTX 5090 in a system using a Ryzen 9 9950X3D, Gigabyte B850 AORUS ELITE WIFI7 ICE motherboard, and 1000W Lian Li power supply. The 5090 is connected with the included 600W 12V-2x6 cable rather than the adapter because I do not have enough spare 8-pin connections. I am also using a PCIe 4.0 riser cable because the card is mounted vertically and does not fit horizontally.
The motherboard has the latest BIOS. I initially connected DisplayPort to the motherboard so I could boot into Windows and use DDU, then planned to reinstall the NVIDIA drivers. After connecting the display to the 5090, the card's lights look normal and there is no warning light on its power connector, but I get inconsistent results: sometimes a black screen with the motherboard VGA LED lit red, sometimes Windows loads but becomes glitchy, and sometimes the screen goes black when the NVIDIA driver installation resets the display. The computer works normally when the monitor is connected to the motherboard video output.
What should I check to determine whether this is a driver, power, riser-cable, BIOS, or faulty-GPU problem?
4 Answers
Using the dedicated 12V-2x6 cable is generally preferable to the adapter, provided it is an original cable made for that exact power supply and it is fully seated at both ends. Make sure the connector is inserted completely and the cable is not sharply bent near the plug. Also confirm that the 1000W unit is rated for the card and that you are not mixing modular cables from another PSU.
The riser cable is one of the first things I would eliminate. Temporarily install the 5090 directly in the motherboard’s main PCIe slot and test it there. A PCIe 4.0 riser can fail to negotiate reliably with a newer card, so you can also force the slot to Gen 4 in the BIOS instead of leaving it on Auto. If the card works directly but not through the riser, the cable or its connection is the problem.
Since you already ran DDU, repeating the driver cleanup probably will not tell you much unless the old driver was not actually removed. First get the card displaying reliably at the firmware or Windows level. Test with the riser removed, use the motherboard’s primary PCIe slot, load BIOS defaults, and check whether the VGA light remains on. If the 5090 still fails when installed directly with a known-good power connection, the next useful test is the card in another system or another GPU in this system.
The motherboard video output only proves that the integrated graphics and the rest of the system can boot; it does not prove that the 5090 is initializing correctly. If you can reach BIOS, set the primary display device to the PCIe slot and temporarily leave integrated graphics enabled for troubleshooting. The key comparison is whether the 5090 works with a direct motherboard connection and no riser.
That is what I am suspecting too, since the system is more stable when using the motherboard display output. I will test the card without the riser if I can reposition the case.