Quote from zdreg:
" Answer
Either the monitor is going bad or the video card is going bad. If you can get your hands on a spare monitor, try swapping it out and see if the lines are still there. If they are, then the problem is with the video card. You'll want to replace the video card if that is the case.
Answer
Ram modules can also cause vertical lines on a monitor.It's hard to believe but i have experienced it multiple times.The ram is detected by the system,yet the display is corrupt.If you open up the pc and touch the ram modules the lines go away.This is very rare yet a possible cause and easily overlooked"