Amanda,
Remove the spark plug wire and place a srewdriver in the wire tip. Lean the wire end with the screwdriver against the engine case. Pull on the starter rope and see if a spark jumps to the engine. I suspect your magneto has failed. An engine needs three things to run: fuel, air and spark. If anyone of these is missing, the mower won't run.
Good Luck!
Gunny63
June 2010