I'm gonna guess its something with the secondary gears or the output shaft, or some stripped splines somewhere. Thats the only thing I can think of if it will shift through the gears and just not move. Unless its just a completely and totally worn out centrifugal clutch, but I've never heard of one being so worn out that the bike wouldn't even try to move at all. At any rate I would say you're gonna have to go into it and do some inspecting.
His: 04 Honda Rubicon, snorkeled, radiator relocated, half Rhino'd, Moose 2" lift with spring spacers in the front 14x7 Highlifter XL2s, 30x10-14 X-Lites
Hers: 05 Honda Recon ES, snorkeled, Highlifter 2" lift, 14x7 Highlifter XL2s, 26x9 Zillas