I am worried that something may be on the way out on my mid-2011 iMac. A little bit of history. It recently had it's HDD replaced and Apple for some reason decided to replace the LED screen as well as they noticed problems... heh? I never noticed anything... anyways... The last week at random times this has been happening. The vertical lines are not always the same. One time I had a white / grey screen with pink thick vertical lines. Weird. Anyone have any idea what could be going wrong? *Update* p.s. when i hard reset the iMac it works again. But who knows when i will suddenly get a white screen of death.