If you get nothng when jumping directly from battery to starter, then either the engine is not earthed or the starter is dead.
If there is no click at all when the key is turned to 'START', then it's likely there is a faulty safty switch somewhere. Make sure the brake is fully applied, and the mower is disengaged before trying to start. Hold the key in START, and move the blade engage lever and brake pedal back and forth slightly to see if the switch adjustment is marginal.
phil_saunders@bigfoot.com
Phil Saunders
March 2009