Four wheel drive not working, front end does not spin

I've had almost no problems with this rig , occasionally stubbornness to move the shifter into 4low , and if I'm bouncing around in 4hi it has a tendency to pop out of 4x4 . Well anyway , after using my 4x4 flawlessly all day , I went to engage earlier and the front pumpkin isn't doing its job , I saw that the driveshaft were all spinning up until the front end . I don't know anything about these solid front end 4x4s , I'm use to the half axles with air actuators . All my fluids are full and clean just fyi . What would cause the front end to not engage when I made sure the hubs were engaged and the shifter was where it was supposed to be? It feels like the transfer case is fine, no issues engaging. Also my 4x4 light is on .