Would you be able to recall the steps you took after physically installing the GPU's? Also for the sake of it, list both GPU's you're using, are they identical?
Lastly it looks like in the manual that there have been cases where after enabling crossfire and restarting, it doesnt stay enabled and it says to go back into the catalyst settings and ensure that it is checked. Sounds silly I know but just trying to help cover all bases as most things that go wrong with computers, atleast for myself, are simple things that got overlooked.