Why does one of my cards (radeon HD 7770 Ghz edition) show as disabled in my crossfire setup. previous cards were 2 xHD 3870 a

Solution
remove the other cards and put the 7770 in the top most pci-e slot.
you cant run the 7770 in crossfire with a 3870 there different a architecture.
you can run a 7770 in crosfire with a 7750 or 7790 only.