how to fix my nintendo ds?

I have an old style nintendo ds. My ndaughters friend went on it using a pen on the bottom screen, she has dinted the screen and now when first powered up it goes on and then off, it will come back on then when you go to play the game it will sometimes but then other times it is as if there is no connection being between the stylus and the instructions on the screen I hope you can help me out as iv got a very upset daughter at the moment The model number is 11512671