Try downloading the VGA drivers and reinstalling them, there is a choice of ATI or intel drivers depending on the exact specs of your laptop (if you need the ATI ones there will probably be an ATI sticker on the laptop, otherwise go for the intel ones)
It's also possible that somebody has been playing about with the colour profiles in the display settings, so worth checking they are all set to default.
If the driver reinstall doesn't sort it and you can't find any problems in the colour profiles then it's probably a physical problem, most likely just a bad connection to the screen, but if that is the case it would require stripping down.