Remove all SDK componets and your 11.3 drivers. Reboot and use Driver Sweeper to clean up the AMD installation files.
Then install ONLY the official catalyst 11.4 drivers, you don't need the sdk.
EDIT: I just found this from you:
I finally got two of my 6990s hooked up and both of them are mining just fine now under windows 7.
but then randomly the whole computer just shuts off, but not completely.
the monitor no longer displays anything and i know they have stopped mining because i checked deepbit.
im using 11.4 cata, not sure about sdk, i never installed any so it might be what ever it is default
its also @ 100 percent cpu and 56 percent ram.
anyone know whats going on here?
Do not open multiple threads on the same topic and try to keep one updated if you want help.