This is really strange. I have come across this problem umpteen times, but it has always been because Family Logon or Client for MS Networks has somehow been removed.
The only other thing that I can think of is that the reinstallation might have removed the user setiings on the computer. Is the computer used by more than one person, and does each user have their own settings? If so, have you checked that your profile still exists? I have never used the multiple user option, but I believe it is set up in Control Panel > Users.
Having had a few pints, I have now developed enough courage to ask the inevitable question, Lona. How on earth did you manage to
accidentally reinstall a whole operating system?