If you are able to log in as Administrator, you can probably fix the
problem. To do this in XP Home, you must reboot the computer, then keep
pressing F8 until the login prompt appears. You may have to type in
"Administrator" in the username field. By default, the Administrator
account has no password in XP Home.
Once you are logged in as Administrator, you can do whatever troubleshooting
you need. I do not know how to restore the account names on the Welcome
screen, but you might try the "NET USER" command. Instructions for the NET
USER command can be found in the Help and Support tool. Just type "NET
USER" in the search area. This command must be run from a command prompt.
To launch a command prompt, go to Start, Run..., type "cmd" then click Run.