call a service person for repair,?
does it crank, does the starter work. or dead silent.?
if starter works , and won't start,check for spark.
is sparks good, use test fuel .
if test fuel fails try checking compression on the engine.
big lawn mowers like this have many safety lockouts. that can fail easy if you abuse it. (or bad luck)]
sometimes hitting stump can break the engines crank shaft or rod.