Certainly sounds like Backlight or invertor
"If you shine a torch on it, at the right angle, you can see that it is all working, you just can't see anything." is classic symptom.
There is no light in the screen. If the screen / connections were damaged then you wouldn't get image as stated.
To use external monitor when in windows you need to press a key combination Fn + one of the f keys the one with the blue sqaure. you may need to "cycle through" - LCD - external only - lcd + external.