1998 Explorer 4x4 problem

I have owned my Explorer through 2 tough Ohio winters and for some reason this last winter I spun out several times and actually wrecked the passenger side of my car from one of these spin-outs. The first year I owned the vehicle the 4x4 worked perfectly, so I don't really know what the problem could be. All the tires are in great condition and when I turn the 4x4 on I can feel the tires gripping the snow better, but I just don't feel safe driving in the snow since I had so many problems this last winter. Any ideas on what could be causing the problem?