Small Engines (Lawn Mowers, etc.): Wont start, mechanical aptitude, selonoid

Question
I am trying to repair our church's lawn mower.  It will not start.  Does not turn over.

I have charged the battery and replaced the selonoid, checked all the fuses, and replaced the spark plug.  I am probably missing one of the most obvious solutions, having a mechanical aptitude, but no experience.

What should I check next?  
Is there a flow chart for troubleshooting this type of thing?

George

Answer
Actually George, there is a flow-chart for this in a repair manual.  The fact that it will not turn over is the most critical.  Can you bump it over by jumping the battery to a car battery?  (DO NOT TRY TO CRANK IT-CAR BATTERY WILL SPIN THE STARTER TO FAST- just bump it)  If it turns over your problem is your battery connections. One of them is bad.  Wire brush pos N neg terminals, AND where the neg connects to the mower frame.  Try it again.

Here is the flow-
1- Verify that the engine turns freely (not locked up)
2- Battery connections corroded
3- Weak or bad battery
4- Electric starter bad (brushes worn out, bearings bad)
5- Ignition switch faulty (check solenoid for 12v while attempting to crank)
6- Faulty wiring (test jumper connect to solenoid)
Lemme know how it goes ok?