I have a john deere la100. Recently I was moving some tall grass but had to get off the mower to remove some brush. I turned the mower off but left the engine running. When I got back on the mower, I put pulled the lever that makes the blades run again but this time it would not. I discovered initially that the belt had came off the spindle and I thought the problem was solved. However, I put that back on and it still does not work. I have had a problem with that happening before and all I would need to do would be to put the belt back on but this time it's something different and I don't have a clue. I'm new to the riding lawn mower thing so if anyone could help, I would appreciate it. Note, I also notice the spindle or wheel that comes down through the engine may not be turning like I should.

Thanks...