Main GPU not working when i use a second?

[__2060__]

Ok so basically i want 3 monitors but my 960 doesent have more than 1 dvi port, so i used an old GeForce 8600 GT for my third monitor but now my 960 is only displaying on one monitor that its connected to and isnt even displaying on my 2nd monitor, why is this happening? Am i even able to do what im trying to do? And yes i have updated my bios, updated all of my drivers, made sure every dvi cable and hdmi was plugged in properly to the gpus, and ive reseated both, ive even tried different pcie slots. help.

 

[pootissandvichheavy]

Full specs? Your motherboard may not support a card as old as the 8600 GT...

 

[__2060__]

Full specs? Your motherboard may not support a card as old as the 8600 GT...

I have an AORUS B450 PRO WIFI and the 8600 GT works fine alone but not when paired with a 960

 

[pootissandvichheavy]

I really have no idea, but my only guess now would be the age span between the 8600 GT and the 960. (about 10 years apart, 9 to be exact)