ORIGINAL: djheptic

i took the car up a ramp and i noticed just the front wheels where wheel spinning on the ramp, and the back ones not moving at all. maybe this is my problem, so i lifted the car up and gave it a rev and all the wheels spun? what the hell? so i took the rear diff appart and noticed the big gear is slightly worn, could this be my problem? ill get a shot of it so you guys can tell me if it is or if its not