Cheryl,
Is the mower turning over? If so, it is either a fuel, air or spark issue. If it doesn't turn over, it could be safety switch issue. Is the mower in gear? Is the PTO engaged? Does the seat have safety switch?
If there is no "click" when you turn the key, it could be a bad ground, a bad starter soleniod or the starter itself.
Good Luck!
Gunny63, June 2010