Screen may have gone - replace screen
Cable may have failed - replace cable
Cable may have come loose - refit cable
Graphics chip may be failing - reflow solder on Graphics Chip
Plug a monitor into it, if the picture on it is fine then likely it's one of the first three, if the picture is the same likely it's the last (unless your setting are all messed up
If you want to pop it down one of them can have a look at it for you.