I've been having problems with my 2011 27" iMac for the past 6 weeks and I was hoping to dive into troubleshooting it this weekend. I only discovered the problem recently as it had gone mostly unused the last 3 years, but I had used it the 3 years prior to that very extensively on a daily basis without issue. It is a quad core machine with 16gb ram. The issue I'm having is that my iMac will just randomly freeze and the screen turns to a grey background that you can see has a pinstripe pattern. It is light and medium gray vertical pinstripes. It turns to this same screen every time it freezes, and so far it has been freezing quite consistently. Sometimes it happens after 10 minutes of usage, other times not till 3 hours of usage. There is no discernible factor causing the freeze. Sometimes it happens browsing the internet, other times running a application, other times just navigating finder windows. It requires a hard restart by holding down the power button to shut off and turn back on. I wanted to post here to see if anyone knew what this could be or where would be good places to start my troubleshooting. I am really hoping that there will be a simple fix for this, but some preliminary research does lead to a potentially bad logic board which would probably just have me cut my losses and just go buy a cheaper desktop PC. Any ideas or things to try? I don't have easy access to Apple stores in my area, but is there a good number I can call for support? Thanks all! EDIT: Pic here: Not mine but grabbed off the internet. My screen looks exactly the same when it freezes.