Small Engines (Lawn Mowers, etc.): LAWN MOWER PROBLEM, briggs and stratton, combustion chamber

Question
Hope you can help me. SOmeone used my lawn mower and told be it was smoking real bad. I got around to checking it out today. The mower will not start. Looks to me like there is oil coming through the exhaust and oil where the spark plug is. The mower is a very new push style with Briggs and Stratton engine.
Afetr further questioning of the fellow that used it he told me he hit something with th emower and turned it upside down. I think somehow turning the mower upside down spilled the oil out of the mower and oil has ended up where it should not be..any suggestions?  

Answer
Hi Tim,

Unfortunately you may now have 2 problems.  If inverted, the mower probably has oil in the muffler, combustion chamber and air filter.  I would check and clean or replace the air filter.  Then check and clean the spark plug.  Once running, any other misplaced oil will burn off.  Check the oil for the correct level before starting.  Now...If it still will not start and especially if it kicks back and tries to pull the recoil rope out of your hand, I would suspect that the flywheel key is sheared.  This is common when an object is struck while mowing.  
Let me know what you find and we will go from there.

Good Luck,
Michael