If the driveshaft isnt spinning then the tcase isnt engaging. Also, the driveshaft will spin with the hubs locked, so maybe you have more than 1 problem. The hubs could possibley be gummed up and not engaging. Take them apart and check them out.
If they werent swapped out you'll have a ttb 44 front and an 8.8 rear (slight chance of a 9").