Acer timeline sceen gone dark

I have an acer timeline laptop as3810t. The screen has gone dark and its almost impossible to make anything out. the info is there but there is no lighting of the screen. I found i could use a torch to shine onto the screen and that helped see what is on there but clearly not how it should be.
Additionally, when i try to start it with an external monitor it works for 20 seconds then shuts off.
Anyone have any idea whats happening? have i triggered some shortcut somehow or is it faulty?
thanks in advance