AutoCAD 2010 :: Images Of Materials Disappear

I have a student version of AutoCAD 2011.  When I render, I can see the materials in the materials browser.  However, when I try to attach them by layer, the images of the materials disappear.  I only see black boxes.  I also get a completely black image when it renders.  There is no image at all even though I have lights and cameras on and in place. I read online that I might need to reinstall the materials library.  I followed the instructions exactly and reinstalled it, all three sections.  Still, I'm getting the same results when I try to render.