I don’t know what to title this, I just need help.

I plan to replace the gpu In my 12,2 iMac 27” with a NVIDIA k2100m. I have enabled what is shown in the photo and now Everytime I turn my iMac on it either shows a black or a white screen. I can hear the fans spinning to life, but the screen still shows nothing. I have not installed the new gpu yet because it has not arrived and I need to do some work with the iMac. Does anyone know how to get my device to boot properly with an amd card installed with NVIDIA Kepler patches? Thank you!