I have M18x with dual 6990Ms...
For the past week I have been experiencing this problem for no reason whatsoever...
Only one GPU is being detected, while the other one is not, neither in device manager not in CCC..
I never experienced this problem before, it just happened out of the blues!
Only if I do several windows restarts it would get detected!
I tried to uninstal the adapters and reinstal a new catalyst...but no use!!!
It is worth mentioning that I had both GPU replaced a month and half ago!