Think the backlight is buggered then...
If you really really want, you could open the screen up. IT isn't all "that" hard.
Sometimes there is a ribbon cable going to the backlight that can get "worn" pressing it etc can fix it. A bit of sellotape has secured and got it working for me in the past... !!
![Cheesy :D](http://www.pc-pals.com/smf/Smileys/Smileys/cheesy.gif)