for mining don't use crossfire! it is for gaming and you could connect cards within the same series (however, the best are two identical cards)
are you using win or linux? i was not able to run 7770+7850 on linux, on win 7 running fine
check if cards are visible in device manager (or catalyst center)
try cgminer only with pool parameters and intensity around 13-14, than maybe add threadconcurrency an so on ...
also use --gpu-reorder to sort cards based on pci-e bus position, than you could set separate parameters using comma (e.g. -I 13,17)
also the first start is bit longer, cgminer must compile some binaries, you could see it afterwards in your dir