Okay, this is bizarre. I was watching The Simpsons tonight in VLC when suddenly the screen developed these strange alternating bars. At first I thought it was a hardware error. My iMac was fresh from the Apple repair shop for a replacement DVD burner and had been running for about two hours. But see the images below. Those are screenshots. So I'm left suspecting that it's some crazy software glitch and not a hardware error. And the odder thing is: Some things display fine except for localized corruption. Look at that screenshot of John Stewart. Just his face is covered with these bars. Although this corruption covers the entire screen, sometimes windows aren't pixellated/blocky at all, they just have a bluish hue to them. What gives? Can anyone guess as to what the problem might be? Have you ever seen anything like this? I've already messed with calibration settings under System Prefs, running through all sorts of options (resolution, gamma, etc). I ran Onyx and cleaned all my caches. Then I reset the PRAM and SMU. I even left the iMac to cool off for about 20 minutes. Nothing works so far.