How can I fix my B&S 21hp mower so it will start?

I have a 3 year old Briggs Stratton 21hp commercial engine in my Husqv mower, and it just stopped running when my mower got jammed up against a trailer that would not budge. It turns over fine with the starter, but acts like it is not firing - just wont start. Never experienced this - did I shear a pin or something?