I began getting this really weird, patterned screen several months ago. It's reminiscent of Windows' Blue Screen of Death because nothing can be done to get out of it except restart the computer by holding down the power button. The odd part is that the color varies from occurrence to occurrence. It can be blue, red, often gray, and tonight, it was green. I can't take a screenshot to show you, but I did take a zoomed-in photo of it with my iPhone. What could be causing this? Over the course of a few months, it has been happening with more and more regularity. And, as far as I can see, there is no pattern. It just seems to happen. I finally got worried enough about it that, last week, I backed all my data up and wiped the hard drive. I reinstalled all the major things that I use with the latest versions available, leaving off extraneous software downloaded from the Web. Other than the standard Apple stuff, I have the latest versions of IBM SPSS, Office, Photoshop, Epson printer and scanner software, and VLC. I am using a 24" iMac from 2008: 3.06GHz Core 2 Duo, 4GB factory-installed RAM, OS X 10.6.7. What could be causing all this? I've searched online and can't find an answer. I will post the photo of tonight's green screen pattern.