HELP! 4x4 isn't working!
 

I have a 96 cummins 12 valve, and the 4x4 went out. The front drive shaft is spinning but not the the front wheels. Please help me. Could it be a vacuum hose???

Could be a vacuum hose, could be the vacuum actuator on the front axle.
Does the heat move from the defrost setting to the feet setting?
Yes? - bad actuator
No? Vacuum leak

Sometimes (for me, I'd go so far as to say frequently) those vacuum leaks are as simple as a line coming off a fitting. The older these rigs get the more it happens. If your HVAC still works as it should, there can still be a leak causing it. There's a double plug on the CAD on the axle which is pretty easy to get at and plug back in with the wheels turned to the left, and two single lines that run into steel nipples on the crossmember for the trans/transfer case that you have to crawl underneath to get at. If it isn't a simple "plug it back in" fix, the most reliable way to know your 4WD is going to work when you initiate it without spending any money is to pin the CAD over, which is essentially the same as driving a Ford around with the hubs locked.