My wife's 20" iMac G5 (no iSight) worked GREAT for 3 years. Then the warranty expired and three months later: Display failed. That is, after turning on the computer we would hear normal start-up sounds, we could change the volume via the keyboard, but the screen was black. After looking here and elsewhere we first assumed: 1. Logic board. This was not the case as we went to Apple store and by resetting PRAM we were back up and running... for 2 days, then black screen once more. 2. Video-card. We went back to the store and the iMac was connected to external display which quickly displayed our video-output. The preferences had been changed to "external display" (don't know how). A Genius installed an earlier version of OS X Tiger and once again we were back up and running. We went home, re-installed updates for Tiger and the next day, after a sleep-cycle, the computer had changed the preference files to external display again. Black screen. Has anyone experienced this before? Did upgrading to OS 10.5 (a 100 dollars cost) solve this problem? Any advice?