Sounds like the transfer case has bitten the dust. Take the front driveshaft off, and try to move it, if stuck take transfer case off transmission. Take the two halfs apart by removing the 14 or 16 bolts that hold it togeather. With a dead blow hammer, tap the sides of case all around until it splits in 2. Take a look inside, bet that the drive chain has wrapped itself around main sproket and jamed between case and gear. Junk yard replacement is most cost effective way to get back on the road.