My Pathfinder starter was replaced but now not turn over

I have a 1994 Pathfinder, which I had the starter replaced in it at the first of the year. On yesterday I experienced the same problem where everything was working, except that it would not turn over. I was able to get it to a shop for repair. According to the mechanic, he replaced the starter and the vechile still would not start, he is telling me that it could be the flywheel. My question is exactly how is the flywheel related to the starter?

The starter has teeth in it that push against the the flywheel that also has teeth. Starter is justed used to "kick start" the engine. If you are missing teeth on your flywheel it will start sometimes and sometimes it wont. THINK OF GEARS OR SPROCKETS. Be sure to check small electrical starting parts also such as your battery. Let me know how things go...ask your mechanic to show you the flywheel if you get the work done. Get an estimate first!!