Motherboard won't display monitor after GPU install

I have a MAG X670E Tomahawk (WIFI) motherboard. I hooked up a monitor to it, and it was displaying fine.

After connecting my RTX 4080 to it, the motherboard no longer displays anything, and it's not even detected in Windows 10. The GPU displays monitors just fine, but I prefer the secondary monitors to be handled by the motherboard.

Have any of you ever dealt with this issue? Any ideas for what I can try? I've installed all the drivers for the motherboard + GPU, to my knowledge.