I just buit my first gaming PC and i have sli gtx 460 cards. When i play with sli enabled, my screen freezes, a buzzing noise occurs, and my computer completely restarts. I have all of my drivers updated, and i can play perfectly fine on a single card. This happens with all games.
Specs: i5 2500k intel sandy bridge cpu chipset lga 1155
16gb corsair vengeance DDR3 RAM
850w XION power supply (which i had to use sli adapters for to work with 2 cards)
ASUS Sabertooth p67 rev 3.0 1155 chipset
Coolmaster haf 912 mid tower case
500gb western digital HDD
You need an SLI bridge for ANY PSU.
Sounds like a flaky power supply or you haven't got all the GPU power plugs in. Have you tried each card seperately? Do they each work by themself?
What games are you trying to play?