I have a 580 with a 480 with my 580 been the master card and I kept getting blackscreens each time I enable sli then a bsod soon after, but when I plugged my monitor to my secondary card it all worked. Try that
This is how I did it,
1) Put both cards in your PC
2) Install the Original drivers
3) Reboot
4) Run the install of the Modded Drivers
5) Reboot
After windows boots up you should be able to activate them in SLI via the Nvidia Control panel..
Finally got GTX 580 with GTX 480 to work..
It used to BSOD on me everytime I enable the SLI.. originaly I had 2 monitors connected to my gtx 580 still follow the instructions but BSOD.. then pulled out 1 monitor still BSOD, BUT when I put the second monitor in the GTX 480 it worked!
so for...