No desktop after logging on

We have are running Windows 2000 Advanced Server. After logging in we do not get a desktop all that shows up is the background. Our users can access the files and programs they need to do their work, and we can bring up the task manager. But when we look at the services that are running explorer.exe is not in there. If we try to start it the hour glass comes up for a few seconds like it is trying but then nothing happens. We have looked on Microsoft’s Knowledge base and done everything there that it said to do and still nothing. Does anyone have any suggestions besides reinstalling Windows, because we really don’t feel like working all night long setting everything back up. Thanks for your help.