Clean all scanner glass with windex or rubbing alchohol. Look for any marks or smudges on the glass. I have seen white out cause all kinds of problems on scanner glass, but it should be easily repairable. You can also check where the paper would feed through if you were feeding from the top tray and look for a piece of paper or something that might be blocking the image from the scanner bed. If the problem shows up when scanning from the feeder tray, try to lay it on the glass, if it happens from the glass, try the tray. It sounds like something is blocking scanner light.