animation problem

I''m writing an importer, animator, and render in opengl for Milkshape3D ASCII files. Got a big problem with the animation part though. I don''t make and god dang sense. Here''s my prob: I found this in a file describing how to animate the joints: // the key matrices animate the reference matrices, so you have to multiply them, // to get the final local joint matrix. The get the final global joint matrix, // you have to multiply them by their parents. Thing is, most of the time either the value of the key (rotation or position) or the reference value is zero. So if I multiply them it comes out zero, and no rotation happens. So what the heck am I supposed to do?