Start by pulling the blower housing off and removing the kill
wire from the magneto.
Still no spark = dead magneto
If it is dead, check the kill
wire for voltage , It is a ground
wire that is either open circuit ( running ) or closed circuit ( stop )
If there is any voltage on the kill
wire it will wreck the magneto .
Go to Husqvarna & get a copy of the wiring diagram for the mower which is in the back of the owners manual.
Try to be a bit careful with the words you use
Crank = to turn
so your engine cranks but does not fire
If you have spark then check the timing key in the flywheel has not sheared.
A small movement in the flywheel will allow an engine to remain running but prevent it from starting.
Check the pushrods are still on the rockers.