Cannot unjoin a domain

We have a computer here at work with Windows XP that is a member of our domain.  All of a sudden, they couldn't access any shared printers or drives on our file server.  We checked all the windows updates, checked her domain account on another computer, and it logged on fine there.  She has a network connection and can get out to the internet and e-mail fine.  When I went to rejoin her to the domain, under "Computer Name" both the "change" and "Network ID" buttons were grayed out.  The message at the bottom below them said:  "Networking is not installed or is not properly configured."  Her internet connection was fine, and I even updated her Network card drivers.  As a last resort, I did a repair on Windows XP, but that didn't fix it.  Does anyone know what to do besides wiping her system clean and doing a re-install?  I think there might be a problem authenticating to the server.  It's like joined to the domain, but it's not.