Hey guys, I need some help. Recently, whenever I leave my 2011 iMac for a few hours and come back to wake it from sleep, it seems as if it's malfunctioning big time. I can't describe it that well, so I posted a video (https://www.youtube.com/watch?v=ybtGW4Oxt34) so you all can see. Basically, it's a bunch of oddly-colored small squares in rectangular sections. They seem to respond/go away/move with the click of a mouse or moving windows. Sometimes, it will eventually go away. But other times, it just freezes up completely and I have to restart my computer. My specs are: 27" mid-2011, 2.7 i5, 12gb ram, AMD Radeon 512mb graphics card. As you can see, I have more than enough free RAM available. I have a 2TB attached WD external HDD. What is going on here? Any ideas? Or anything to at least try? I'm getting worried because my AppleCare recently ran out this summer and I don't want this to be an end to my computer!