Use BAMT or upgrade to Windows 8.1.  I had issues with Windows 7 getting 5 cards to run.  Windows would recognize all 5 cards but one would have an error 43 and would not install the driver correctly.  Once I installed 8.1 it had 0 issues.  BAMT is also a good choice but you cant underclock the cards.  How do you have the PSU set up on the cards?  I would run 1 PSU with the 2 main cards and then another PSU with your remaining cards.  Might be a power problem.  Try 1 PSU with 2 cards then add 1 more card on 2nd psu at a time.