Have you had the lawnmower tipped over recently for eg cleaning.
If so it is possible that fuel or oil has entered above the piston and hydraulicly locked the engine. Remove the sparkplug and check for fluid in the spark chamber. If fluid is present put some rags etc infront of plug hole (to catch any mess) and try to turn engine with pull start. If this has freed engine pull it over several times to eject all the fluid. Clean & replace the plug and try again.
If no fluid is present then the engine has probably seized and will need major repair or replacement.
I hope this helps
Robin S, August 2008
