The 4x4 doesnt work in my '97 Hardbody XE

I have a 1997 Nissan Hardbody extended cab pickup with the 2.4 in it. I tried to go muddin in it a while back and I realized my 4x4 wasnt working. The truck has manual hubs and they were locked in so that's not the problem. The floor shifter was in 4Hi, the light on the dash was on, and the front wheels still did nothing. Then a while later my father and I were messing with it, and the 4x4 kicked in. Ever since that one time the 4x4 has not worked at all. The thing that gets me is when it is in 4Lo the RPMs still rise fast and it acts like the truck has engaged 4x4, but it hasn't. I have looked at where the shifter meets the tranny/transfer case and have found nothing to be wrong. It all looks fine, but the front wheels WON'T spin. Can somebody please throw ideas at me as to what the problem could be?  

Is the front drive shaft spinning? Any unusual noises?  

There's no unusual noises and i haven't checked to see if the front driveshaft is spinning or not  

to be honest if there is no irregular noise coming from the front and everything else seems with in reason, "normal". then it sounds like there maybe an issue with the shifting fork in the transfer case, if you lift the front end and turn the drive line, do the wheels turn if so i would definitely look at the shifting fork in you transfer case i would say the issue lies there. they can break or wear.but if the rear end is shifting to 4 low it is also a major possiblity that, that the chain broke in you transfer case, the chain transfers turning force or torque and power from your main shatf to your front wheels/drive-line normally a 1:1 the transfer case contains you gears so thats something else to look into, no if your driveline turns but the wheels dont then might be a ring and pinion issue. but i am no expert. let me know.