I have replaced the Ignition Modular Switch 2 times the car wont start on 1994 Pontiac Grand Am

the car will crank but wont turn over.I was driveing down the road & it just stopped running.When it was running after the part was put on it was cutting out.If its not the ignition modular switch then what could it be?

Asked by for the 1994 Pontiac Grand Am