Small Engines (Lawn Mowers, etc.): Lawnmower, plug hole, oil level

Question
I have a Craftsan 5.5hp lawnmower model #143.005504 self propelled. When I attempt to start it the pull cord is RIPPED away from my hand. The eng. will not start however it will spin. Please help
Thank You

Answer
You either have a sheared flywheel key, a loose blade, bad blade adapter or may be gas in the oil causing the engine to hydro lock.  

Have you recently serviced any components on the mower including sharpening or changing the blade?  Is the oil level correct?  Does the oil smell like gasoline?  When you remove the spark plug and pull the string, does any oil shoot out the spark plug hole?  Have you  or some else recently hit anything while moweing?

Let me know.
Eric