Has battery got sufficiant power to 'throw' solenoid & engage starter?
You could try jump starting it like you would a car.
Or have you checked around the safety cutout circuit.
Most machines have safety switches etc to stop mower being started eg in gear, blades engaged etc.
It would only take one of these to be faulty or a wire to have come off to stop your machine going.
Hope this helps
Robin S, September 2008