99 gmc 2500 4wd push button - front tires won't turn in 4wd

i have a 99 gmc 2500 sierra push button 6.0L. When i push 4 hi or 4 lo my front tires lock up and won't turn at all. It sounds like the transfer case is engaging however the truck won't move at all when in 4WD. The front tires just drag. Is it the axles? Any help would be appreciated.

If the d'shaft is turning the issue is in the ft diff, if the shaft is not turning it is in the transfer case.