Hi! My iMac's screen started going black a few weeks ago and it got progressively worse (ie restart wouldn't sort problem out) so i dropped it in to my local apple dealer and they had the mother board replaced. Since I got it back though the problem isn't 100% gone. Now it wont start up properly from shut down - the on light lights up, but there's no chime and a black screen, so I need to try again and second time around it'll work. This seems to be connected to the last problem i had. I intend to drop it back in for another repair, but i just wanted to get some opinions on how common a problem this might be, what i should expect apple to do about it and how angry i should be, because i think it's pretty bad. i'm just glad it's still under warranty. Any views on this? Thanks a lot!