Hello, I have 2x8800 GTS's in my system and they worked wonderful in SLI when I was running vista, I installed the win7RC for awhile to test it out and right before I installed win7pro I realized that my sli wasn't working at all, the os didn't even recognize the 2nd 8800 card. After installing win7 i updated the bios to the latest, downloaded the chipset drivers from asus and the latest nvidia drivers for the cards and still It won't recognize the 2nd graphics card.
I've swapped out the 2nd card and replaced the main card and visa versa, both cards are functional. It's not a power supply issue as I use a 750w and hardware didn't change from when I was running SLI just fine for a couple months or more in vista, so I'm guessing its a win7 issue or some driver asus doesn't list that I need to go find or something. Any Ideas?
Edit: Man I typo like crazy.
Asus P5N-D Motherboard
quad 2.83ghz 12mb cache intel processor
4gb 800mhz ddr2 RAM
2x Nvidia 8800 GTS cards
1x 650gb Western digital caviar black(i think) for the main drive
1x 500gb western digital for the secondary drive
and a dvd-rom
I have a P5N-D as well, been running good since 2008 (SLI). I never had any problems with the P5N-D but I had the same problem you're having with a 780i. After playing with it for an hour or two (re-seating) the 2nd card was detected. I decided to RMA the board anyways, clearly it had issue. It came back from RMA and never had that problem again, I suggest you do the same thing......send the board in to be repaired before your 3 year warranty runs out.