so anyways i broke down and reinstalled windows. the card initially worked, would mine and such with no problems. so i plugged in my other cards... and it no longer would work. neither would the other cards. and even after the 5850 was unplugged the other ones still wouldn't work.
so at this point i'm at a loss, but i'm probably just going to sell the card on. furmark tests on it check out and it works fine as a graphics card for display and such, but something is up with mining it.
now to reinstall windows yet again to get the original working cards, working again. yay.
I know its not such a big help but I had the same problem when I tried to combine a 4870 with 2 6970... it didnt work... the 4870 worked alone and the 6970 together but not all three at the same time. I couldnt solve the problem.