You may have already checked this out, but I had a similar problem with a Dell monitor and it was definitely the monitor. Changed video cards and machines, and the problem only got worse. Started out as a line, became a narrow vertical red band, eventually ate up the left 1/2 of the screen. Was told that it would be cheaper to replace the monitor than to pay $200 or so to get it fixed -- and still have a 3-year old monitor.