remove and inspect, the bolt de-threaded for a reason.

 

Sounds like the remainder of the original key is still in the keyway.

+1 for take it all apart and inspect for damage of the keyway and the crank threads.

You don't say which engine you have but the pulley bolt changed with the A4, it has different threads and is much longer. I don't think I've heard of it happening with the newer set up so I'd like to know what engine you have.

 

my motor is the a4. this was the events that took place. i was drivin it and for some reason my belt popped off late at night, and i didnt realize at first that the pulley was loose. i got the car on a dolly and got it home and it sat for a month or so then i went to put the belts back on, and when i cranked it over is when i realized the balancer was off. what my buddy said might of happened, is when i cranked the motor with the balancer off and key loose, it might have allowed a gear to crank inside, which is keeping me from sliding the key all the way in. are we on the right track here?
oh and the key isnt broken, it still has the one tapered side and the other side still looks factory and its straight so i know thats not holding it up