My word doent is symbols now?!?

So i made this 5 page long paper about animals tights at school. my teacher told me to save it as a rich text doent because my computer at home runs on windows 7 adn teh one at school doesnt. So it worked for about a week and i finished my paper then i go home today adn tried to open it and it has turned..into a bunch of random symbols! like wtf do i do i need taht paper tommorow and i cant rewrite it overnight. i tried explainging to my teacher but hse wouldnt listen. is there any way i can restore it back to its origional. and why is it doing this (for futur refernce)