Hey i have a 5777, a 5850 and a 7770.  i am running the mobo and the 5850 on one psu and the other 2 cards and all the fans on the 2nd psu, any 2 cards will work but as soon as i add the third card windows hangs during boot,  i can run the 2 cards on the main psu (520w) and it also works if i try all 3 it hangs so i figured it was lack of power now i added another psu (500w) i have gone as far as to try

1 card on the 2nd psu
2 cards on the 2nd psu
3 cards on the 2nd psu
all cards are independent but have tried sli and no dice

my best guess it it is a driver or something but all the drivers have been installed and are fully update

each sli spot has also been tested and like i said it is the 3rd card that kills it =(  

any recommendations would be AWESOME

thanks.