Hmm.. I've similar situation, and I think I found reason. I have installed Daemon Tools. When I mount any image and reboot computer, Windows hangs on logo screen. When I mount and unmount image before reboot, Windows boots properly. Question is what is the problem - registry (image information is kept in registry I think) or virtual device? Problem didn't occur few days ago, althoug configuration (programs, CD image) was the same. But meanwhile I used program named Ntregopt which optimized my registry (and decreased it size by about 10%). Maybe this is the problem?