When I first bought my iMac I was very excited than it just passed a year and it was a hard drive problem with a question mark appearing in the start-up screen. I replaced the hard drive and one week ago the display of my iMac was going off everytime but still the computer and the disks were running normally. I sent it to the nearest place to fix it. I haven't got it back yet, I am going to get it tomorrow but I need your help guys... What can I do to prevent my iMac from going crazy for the third time ? I mean... what's the problem ? Thanks.