|This sounds like something in the operating system has become corrupt.|
First and foremost, I hope you do regular backups because you may need them. If possible, I would copy that drive onto something else as a backup. Image it onto a NAS, another computer, or an external USB drive if possible.
You can try a "repair" of the OS. This involves booting to the operating system as if you were going to do a clean install of the OS. Go through the setup process, past the "recover console" and to the point where the install process sees the existing installation of the OS on the HDD. You should then have an option to "repair" the install.
This will basically reinstall all Windows files and if successfull, will require you to rerun the latest SP and then do updates as all SP's and updates will be lost.
I've had to do this in the past on several PC's and it worked nicely. I see no reason for it not to work on a 2000 server.
NOTE: This is a "last resort, I've tried everything else" procedure.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.