2001 sportsman tranny issue

2001 sportsman 500 4x4, i dont have a high gear, i have reverse and low gear, but when i put it in high gear, i hear and feel it click into gear like it always does, but then i hit the gas and it moves half an inch then pops into nutreul, any ideas on what it may be, something internal, a linkage or something, any advice on where to turn to would be helpful