I had exactly the same problem with my server. The advice I was given was to reinstall over the top of the existing installation. As I had installed SP3 and the install disk was without SP I didn't do it, for fear of making things worse. In the end I dumped the server. Sorry, I know it's not the answer you were hoping for, but I wasted a good few days trying to solve it, and it worked out cheaper in time and money to rebuild.