having issues

the front wheels work in 4×4, but the not the rear wheels. it is like they won’t engage, neither in 2×4 or 4×4. when i take the 4×4 off and go into 2×4, the front drive shaft will spin.

i understand without breaking it down, i won’t know for sure. i am not a mechanic but am somewhat mechanical. i think it has to be either a drive shaft/u-joint issue, or a gear issue. i have not tried to see if the rear wheels engage when in reverse (can’t remember at the moment), will try later on when i get home.

any help is much appreciated.