What you described could either be due to a sheared flywheel key, or is symptomatic of a clogged carburetor. If the engine stopped abruptly (due to the equipment striking an object) and has not restarted since, you likely have upset the ignition timing and caused a sheared flywheel key. To have this repaired, please visit with your local B & S Authorized Dealer: http://bit.ly/14yWuSi
If that is not the case, then you may have fuel that is going stale and clogging the internal carburetor passages. Fuel can go stale (turns into a varnish) in as little as 3 weeks.