Hi. My son just got a hand-me-down train from his grandfather. It has been in a box, in a closet for years. It's an American Flyer 21165. Anyway, we had it cruisin around the track on our first attempt. But, now it seems the wheels of the engine only go in reverse. This question may sound silly, but I'm real new to this. What happened?? Any help would be appreciated. Thanks!