So for three weeks a perfect iMac. Non f the yellowing or flickering at all. Last night was online and half the screen went see through grey and then blank. Tried restarting the computer and nothing. Faint sound of starting up ie drives and thats is. Screen is not coming on at all. Called a Apple care this am and was told to take it to the Genious Bar today. Appt set for 1430. We shall see. I have a feeling that I am up a creek without a paddle. This is my first Mac. Not happy that this has happened!!!