Make sure the cutting desk is in the disengaged position. This is labeled on the bottom of the mower, near the seat.
Check that the brake is not set. This automatically disables starting of the mower.
Make sure the 12209's battery is installed properly. Use a voltmeter to ensure the battery is charged fully.
Inspect the fuse box, near the engine, to make sure the fuses are not blown. If they are, replace them.
Check the gas level to make sure there is enough to start the 12209.
Make sure the spark plug wire is not disconnected. Replace the spark plug if it has burned out.