Small Engines (Lawn Mowers, etc.): Lawnmower Pull Chord wont pull out, spark plug, belts

Question
The pull chord on my lawnmower won't pull out.  The engine doesn't turn.  It appears the engine is locked. I made sure the blade is unobstructed and have even removed the blade.  This lawnmower is old, but in good working order.  There was oil in it and the spark plug is new.   The belts look OK....Please help.  What should I try or troubleshoot next?

Answer
Remove the spark plug and see if the engine will turn over.  I find a lot of engines with oil in the cylinder that prevents the rope from pulling.  Good call on removing the blade...that's also a common area that will prevent the string from pulling.

Next I start with the blower housing/starter.  Start removing parts to see if any of them are causing the engine not to turn.

Do you have a riding tractor or push mower?  What brand of engine?  What brand of mower.

Let me know.
Eric