I own a 17" g5 imac and today I was just browsing on Firefox and all of a sudden the screen became checkered with thin pink and white lines. It is most noticeable on the menu bar and anything that is grey or white in color. It is not checkered on the blue background behind my desktop photo. I have an external monitor plugged in as well and the same thing is happening to that monitor. I have a powerPC imac G5 OSX 10.5.8 1.5GB DDR RAM ATI Radeon 9600 Here is a screen shot: Haven't reformatted it yet. Hope there is a better solution. Purchased it used about a year ago. No warranty.