one of three things: lack of fuel, lack of spark, lack of compression.
Start with lack of fuel. Remove engine air cleaner. Have assistant try to start engine in normal fashion. Spray several shots of rattlecan carb cleaner directly into carb throat while engine is cranking. If engine attempts to start or "pops", you have a fuel delivery problem.
Ignition: obtain inline spark tester from tractor shop or remove plug and ground to engine block while cranking - look for spark at plug.
Compression: Attempt to turn engine by hand with all drives disengaged. If flywheel turns easily with little/no resistance OR won't turn at all, most likely there are internal mechanical problems.
Post back with results of above tests and we can proceed from there with hopefully best fix.

Fuel cap vent ?

rcbe and tomplumb,

Thank you both for your speedy replies. I went out this morning and checked and cleaned the vent cap. Then I squirted carb cleaner into the carb, and voila; it started right up; and is running fine! I always seem to panic when something mechanical happens; and I overlook the obvious.

Around here, they don't call me "The moron with a screwdriver" for nothing! Thanks again!

Really? They call me Mr GoodPliers....

rcbe and tomplumb,

Thank you both for your speedy replies. I went out this morning and checked and cleaned the vent cap. Then I squirted carb cleaner into the carb, and voila; it started right up; and is running fine! I always seem to panic when something mechanical happens; and I overlook the obvious.

Around here, they don't call me "The moron with a screwdriver" for nothing! Thanks again!