Small Engines (Lawn Mowers, etc.): engine wont start, engine model type, battery cables

Question
I have a fully charged battery, but the engine drags and won't start

Answer
If you remove the spark plug will the starter turn the engine?

Did you disconnect and clean the battery terminal posts and battery cables with a wirebrush?

What engine do you have?  What is the engine model, type and code/serial number?

Let me know.
Eric