ocassional screen failure

I have a dell latitude D430 using windows XP. It has developed occasional screen failure..no light ,nothing.
When the screen is working,there is occasionally some slight flickering on the screen and a hint that it is affected by moving the screen back and forward so I'm thinking faulty connection. But when the picture is totally gone, if I plug in a monitor it has the picture, then I fn8 again and my screen is on, I can disconnect the monitor and the pc screen is ok again. Any ideas about whats happening. Thanks