BF3 seems to have a lot of reported issues w/ dual card configurations.
My SLI 560 GTX's were having the same problems. I would start up the game and either it would hard lock when the blue "blinking" indicator would come on the screen, or it would crash out extremely quickly. I did some digging and found that for some reason this was fixing it for a lot of people.
Now, that probably only applies to EVGA cards, but it fixed my issues. I can run it fine now in SLI as far as stability. Not as high performance as I'd expect, which a lot of people report that, but overall it's improved my stability to where I haven't had any crashes in a few days that weren't server side issues. Why that fixed it I don't know as the current NVIDIA drivers are supposed to have SLI profiles for BF3 and all that good stuff, but whatever.
Unfortunately for the overall thing it appears to be something with the game itself and will need to be sorted out by EA/DICE, but hopefully it is soon.