john deere lt133

I went to go start my LT133 for the first time this season, and the starter just spins but doesnt turn the engine over? It worked fine last year no problems? What should I do to try and fix this? Is the piece with gears on it that engages just sticking and not moving out to spin the engine over...

I replaced the drive belt and test drove prior to replacing mower deck. Worked great. Replaced mower deck and test drove without engaging blades. Worked great. Engaged blades and the tractor lurched forward and will not stop or shift with clutch/brake unless I disengage blades. ???????!