4x4 not working

 My truck won't shift into 4 wheel it worked fine all day yesterday?  Any suggestions?

Is the 4x4 shifter on the dash or floor mounted?

Its manual 4x4 the shifter is on the floor.  Can you help? 

I'm assuming the stick will physically move into 4Hi or 4Lo and that when you do that the truck still drives as if it's in 2wd. On thing you can try is to shift the tranny into N then shift then select 4Hi or 4Lo. Then drive forward. If it doesn't work, try reversing about a foot and see if it engages. If that doesn't work, try locking the hubs manually. If none of this works, check your fuses and crawl under the truck to see if any wires have come loose on the front axle or t-case. A fuse that has nothing to do w/ the 4x4 that's blown might adversly effect it. If none of this works, you'll have to go to the dealer or a 4x4 shop and have them look at it. It could be an internal problem in either the t-case or the hubs. Hope this helps.

One more thought....check your vaccume lines. They automatically lock the hubs for the shift on the fly feature. That could be the problem. But if it's not engaging even after manually locking the hubs, then that's not it.

I serviced the hubs and it actually worked, thank you for yor help, I really appreciate it.

No problem. Glad it all worked out. Just out of curiosity, what did the problem turn out to be and what's the mileage on your rig?

I just took the hubs apart, cleaned them with tranny fluid, greased them and everything was fine after that, they have a nice"click" now when I lock them, I don't know if it was the actual hub assembly or the outer ring restricting travel but they work fine now thank goodness it was a quick cheap fix.  180 000km.