Put it in 4x4. Lift one front wheel and block the others. If the lifted wheel can spin, look to see if the driveshaft spins. If it does, the problem is in the tcase. If not, then it's in the front diff, IF no-one swiped the front axle shafts. You should be able to see the axle ujoints behind the wheels. They should spin with the wheel. If not, then it's a hub problem.