1. Fred's right about trying another computer, but you still may have wrong/ old driver- download demo version of Vuescan at www.hamrick.com and see if it's your software.
2. Partially blank pages can appear when you don't have sufficient memory for the scan, but that usuall loosees the lower half of the page.
3. The lamp is probably not the problem, because there is enough liht bouncing around in mostflatbead scanners that you would just see the image "fade"to black, not have a distinct line.
4. best bet is that something inside has come loose and is covering half the scanning sensor, or the mirrors that reflect the images to the sensor inside