White line across screen

Hi,

I turned my macbook pro on yesterday and there is a thin white line that runs horizontally across the middle of the screen.
I've not dropped it or closed the screen hard or anything so not sure why it has appeared.
I suspect its dead pixles or something similar so don't think there's much I can do but I thought I'd ask you guys anyway in case there's something I don't know..
I've had my macbook pro for about 4 months now so it's probably still under warranty..hopefully

Definitely use your warranty. Call Apple and make an appointment with your local genius bar to have it looked at. It could be a graphics related problem or even the LCD itself. Let Apple sort it out for you.