My 667 Powerbook G4, which I bought several years ago, has ran perfectly well up until about a year ago. At that point, my screen began doing strange things, such as the screen will flicker, and horizontal lines will appear on different parts of the screen, and can be refreshed through certain methods such as minimizing the window. Also, sometimes a checkboard of black boxes will appear over the top inch of the screen, and can't be removed unless the computer is restarted. The boxes are only on the background, so windows can go over it. I'm not sure if this problem is common or rare, but if anyone has any info on it, I'd be pleased to hear it. Thanks!