Advent 7013 Black Screen

Question

Having a problem with my Advent 7013 Laptop. The screen will some times go dark. The image is still there only the backlight is not on. This is fairly random and pressing the Hibernate button switches the backlight on again as it shuts down, very annoying. Next time it starts up it is fine and will continue to work for the rest of the day, often the new few then it does it again. I have formatted the hard drive and re-installed windows XP but this has not helped.
Any ideas?