Why my tablet won't turn on

The model of my tablet is Lenovo A3300 GV. I bought this tablet last year June 2014.

I was using my tablet while it was on charging I just download some movies and I leave it for a while, when I came back my tablet won't turn on. What should I do? How my tablet work again? My school files is in internal storage and it has my important files. I don't want to format it. huhuhu..

P.S. sorry if my english grammar is wrong.