Could be the gear seized on the shaft like happened to mine. I lost neutral. Also had an issue with a screw coming out of an aftermarket clutch basket that backed out until it jammed it up. Another time i had the little spring come off that works the shifter. You have to pull the clutch and see if the mechanism is working right, first. it could be easy to fix, worst case is you will have to split the cases.
Will it go when you let out the clutch or does it die?