Was going to post on Apple, but their community pages is still down! I upgraded my iMac '27 i7 (2009 model) from Lion to Mountain Lion. First day in, everything smooth and felt better than Lion. Second day, it all went wrong and I can't use it at all. There's some major flickering and distortions going on, to the degree it's not usable. Usually after about a minute after it has restarted and the flickering goes on, it goes black, and sometimes the 'Major problem has occurred, hold down the power button to restart'. Very disappointed! Any thoughts? I have done the CMD+R and tried to repair disk, disk permissions, reset PRAM. No use. Anyone experienced the same?