Are you really sure its the mainboard that causes all of the trouble? Or could it be a software issue or another hardware issue?
Well it's just a guess from your description of the problem, first step for you is to make sure it's not hardware (motherboard compatibility) issue by upgrading to latest Bios firmware. You can contact your motherboard manufacturer and perhaps they can guide you to right bios update and perhaps also help you figure out, why only installing GPU freezes everything.
As I said I tried to update the BIOS but its not possible as windows says the program is not compatible. I was on the official page. But Ill probably will post this on superuser, thanks for the advice.