I have a Dell 2400MP projector that had the same problem of vertical white lines appearing over the screen.
This may seem like a simple solution, and I don't know if this will work for you, but the way I solved the problem was simply to press the bottom side of the projector, until the white lines disappear . Until now, the problem has yet to resurface.
Here's some simple steps:
1. Turn on projector
2. Connect projector to computer
3. Focus projector
4. If white vertical line appears, firmly press underside body of projector
5. See if vertical white line disappears
6. If not, try slowly pressing other parts of the body of the projector and see if white lines disappear.
7. If solution doesn't work, you may need to send it to the service center.
Hope this solution works for you.