It only takes one hub not locking in to give you no front drive. Put it in 4wd, lock the hubs and then jack up one front side at a time and try to turn the wheel. Make sure it is in park. Does the wheel turn? If it does see if the axle is turning on that side, if it is turning then see if it is turning in the opposite direction on the other side. If it is then the problem is the other hub or outer u-joint. If one side is turning but not the other you have blown the rear, most likely the spider gears.
Another way to check is to put the truck in 2WD, neutral and lock the hubs. Crawl under it and turn the driveshaft by hand, what is turning and what is not? Make sure the truck is not running while you are under it.
Rick