Alex - the first thing I would do is drop it on the floor. This is what a certain reputable gentleman did recently with an engine of mine which wasn't running. As it was explained to me, sometimes dropping it knocks everything back in place. The gentleman obviously knew what he was doing because the engine promptly ran when placed on the track! 
-Greg
P.S. Yes, my engine was dropped, and yes, it initially ran when placed on the track. The rest is my embellishment because I have a sense of humor. It goes without saying dropping it was an accident and he couldn't have been more apologetic. 
