87 k10 trouble

[74 shortbed 406]

I have an 87 1/2 t 4x4. I just bought the truck today and already having problems. I ge the truck home and pull around by the shed, it was muddy so I had it in 4wd. Well everything was fine until it started to sin a little bit then I started turning right, I heard and felt a couple pops and stopped. I put it into revers and backed up into my driveway. I played with it a little and now it wont enven lock into fourwheel drive. It has auto hubs and I think that is my problem. What do you all think. I haven't dug into it to deeply because it got dark and I didn't have time.