00 Ranger 4x4 not engaging
 

I have a 2000 Ranger 4.0. During the last snow storm, I noticed I had no traction. When I turn the 4x4 knob I hear it click and it sound normal like it will engage but the 4x4 does not work. No warning lights blinking. Anyone ever have this problem. (the truck has 93000 miles on it.)