I lost front wheel drive when one of my CV joints blew apart. The inner cage that holds the balls in place in the CV cracked and one or a couple of the ball bearings fell out and that was enough to loose front wheel drive for me. I would visually inspect the CV boots and (with gloves on) squeeze and pinch the boots to make sure there are no loose parts tossing around inside the boots.

I doubt seriously you have transfer case problems, it would not be the first time, but actually transfer case problems are rare on the VX.