How long have you had these green lines in your laptop?
Have you tried reinstalling your drivers?
Edit: You could also try using your VGA port to output to another screen to see if you still get those lines. The VGA port is usually blue colored and has a 15 pin female connector, it's also called D-SUB. Sometimes it's black as well.
If that doesn't work -i'm guessing there's something wrong with your screen/ or video. The only way to fix that would be by sending it in to dell and it may not be cheap if your out of warrenty.