I have a Powercolor HD 6790 and I have this damn problem too. Actually no problems with the games such as BF 3, Crysis 1-2, Nfs the RUN, Dirt3 etc. But Fifa 12, Heroes of Might and Magic V, Hot Pursuit and the Witcher 2 give randomly black screen or gray screen with vertical lines. I tried Catalyst 11.10,12.2,3,4 and 7 Beta but no luck. I wonder if AMD driver team is aware of the problem or not.. Oh how frustrating!