[johnsjmc]

I think you have a hydraulic lock. The oil in the cyl is not compressible and the engine won,t turn over because of it. Remove the plug and try starting with the starter If it spins the motor fast it will blast the oil out through the plug hole(good idea to cover it with a rag to minimize the mess) .Put a teaspoon of gas in the cyl and then blow it out to get the remainder of the oil out. A new plug and it should start. I would also clean out the air filter because that is probably the path from crankcase to cyl thru a crank vent when turned upside down.