Help!!!!!

My 4 wheel drive is not working. When i go to lockit in it acts like i have the brake on and cant move. I can move a few inches but i hear a cruching sound and it is hard to get it back out. its fine when the 4 wheel drive is not locked in. Its a 96 v6 please help

Sounds like something's broken in the front end. If you have Automatic Differential Disconnect (no manual hubs), it's probably the front driveshaft or differential. If you have manual hubs, could be the above or a CV shaft. This is complicated stuff and if you're not a good mechanic then take it in to one. Not very common for this stuff to break, but I can't think of what else could make it do that.