Question Not posting into windows with a different GPU

[Qelzyy]

I don't know why but when I switch from my GTX 1660ti to my GTX 660 (testing purposes) I start up my PC and all the fans are spinning but there is nothing on the display, I tried both HDMI and Display Port and still no post, I took the GTX 660 from a working pc already but just doesn't want to post I made sure the GPU was fully in to the pcie slot and had a connector for extra power from my PSU, and both cards work normally but I just don't quite understand why it isnt booting.

 

[johnbl]

clear bios and attempt reboot.