If I had to guess, I bet one somehow got knocked off the spindle, the guy that owned it (not my friend that gave it to me, but the guy that would have traded it in) got frustrated, forced the tray open which knocked it off the drive gear, then tried to shove another game in to try and make it work.
Basically, what an idiot or 9 year old child would do. Or an idiot 9 year old child.
The belt is intact and as long as the motor isn't torched, then I'm pretty much positive that it will live again!