Small Engines (Lawn Mowers, etc.): Lawnmower fix, sears craftsman, new spark

Question
I have a Sears Craftsman gas mower (12 years old-don't know make and model number) that won't start.  It doesn't crank at all or try to start and then choke; it acts as it does when the spark plug is disconnected.  I've replaced the spark plug, but no luck.  I do notice that the back of the new spark plug is now covered in black oil, however.

Earlier this year I cleaned out the carburetor, changed the oil, air filter etc., and it did run fine after that, but now--nothing.

The mower is 12 years old.  Is there anything I can do to try a fix, or should I purchase a new one?  I'm reluctant to invest in sending it to a repair shop, because the cost would probably be half (or more) of a new mower.

Thanks for your help.

Answer
 Hello L:

 It may be Something Simple. Remove the Spark Plug. Wrap a Wire Around the Plug Threads and Attach the Other End of the Wire to the Engine. Turn the Engine and Check the Plug for Spark. If you have Spark at the Plug, then Remove the Air Filter and Pour a Small Amount of Gas Into the Carburetor Throat. What does the Engine Do? Send me the Model Numbers Off of the Mower and the Engine, Please. With these I can Locate a Breakdown/IPL and Better Assist you. Thanks.

 Respectfully

 John