I recently had to perform a system restore on a Windows XP computer, and now the system's user can't access our Windows Server 2003 domain. What happened?
System Restore has a few irritating quirks, and you've run into one of them. Fortunately, this one is easily resolved. By default, XP users must change their domain password every 30 days; my guess is that at least one password-change interval had passed on the system in question. When you performed the restore, you returned the system to a restore point that was saved before the most recent password change. This created a conflict with information stored in Active Directory (AD). In your case, the password stored on the local system was probably reset to an earlier password. Therefore, the password no longer matches the password stored in AD. Remove the user from the domain, then add the user back to the domain. For more information about password-related problems that can appear after you operate System Restore, see the Microsoft article "Issues with domain membership after a system restore" (http://support.microsoft.com/?kbid=295049).