Sounds like you have checked all the right stuff, time to check the start circuit and starter.
I do this by using a piece of wire at the starter, jump from the large lug to the start post, which is the smallest wire on your starter. It should be white/green. If there are two tan wires, the start wire is the larger one of the two.
If you have power from your battery going to the large lug on your starter, and you jump fro that large lug to the start terminal on your starter, the starter should spin. Make sure the key is in the off position here and be careful, that the engine does not start and the machine does not move on its own....=).
If the starter does not spin, you either have a bad starter, or the engine is siezed up someway. Usually a starter problem, and the simplest and fastest thing to do is replace it.
If the starter does spin, the problem is in the start circuit, there is no power coming down the start wire to your starter, but get a helper and a test light and double check that. There is a fuse, as you know, and a start realy, and wire that could be broken anywhere along the way.
Probably the starter, sounding like to me and in my experience, get back if you need more help.