PC won't give video out with Nvidia GPU's, only AMD GPU's

[GTheGecko]

Hey,

I have a Ryzen 1600 with a MSI b450i gaming plus ac itx board. I was running this with a GTX 770, but I want to sell this pc so I opened it and cleaned everything. After putting it back together, it won't show video out. USB devices work, but no video output. Using my spare AMD R9 280 I boot fine and everything works. Putting my GTX 770 in a different PC, it works fine. I tried using a spare GTX 750ti that works and with that still no video out. The motherboard shows VGA light on MSI's ez debug leds. Unfortunately, I can't plug a mobo speaker to hear beebs, but it's definitely a motherboard problem. I've already tried resetting cmos, DDU'ing drivers, reseating cpu & ram, etc. Thanks boys.