First you have to describe the symptoms. "Doesn't start" can mean a lot of different things, and the parts you listed are all over the place in different systems and will cause different problems. The starter will cause a failure to crank the engine. Of course it won't start then. If the starting system is okay and the engine cranks normally, the crankshaft position sensor or Engine Computer can prevent the engine from running. That can also be called a no-start condition but it has nothing to do with the starter, generator, or battery. The generator isn't even in the picture yet. If it is defective, which GM has a lot of trouble with, the battery will run down very quickly and not be able to crank the engine. That is also a no-start condition but it has nothing to do with the starter.