There are approx 4 reasons why this might happen:
- The backlight has gone (Find a dark place and shine a torch into the screen and see if you can see an image in the background, if you see an image then the backlight has gone) - Needs a new backlight (Engineer to remove and fit) or have a new panel fitted.
- The panel has died - Need a new panel
- A cable has worked itself loose or is broken
- The inverter has gone - Need new inverter
- Long shot, the bios has got corrupted - Engineer could re-flash the bios
- Long shot, Mainboard onboard graphics has gone - Need new mainboard
My personal opinion is that the backlight or inverter has gone - Either way it needs to be opened up to repair it, consult a service centre and get a quote or repair it yourself if your up for it.