XP: Lost admin password

Hello.

One of my users did something to his laptop settings(Windows XP Home) and the usernames were vanished from the initial start up logon screen.

I pressed control+alt+delete and tried to logon with the administrator password but he does not remember the administrator’s password. He does not remember even his account’s password. He told that he just clicked on the icon and he was getting access. The system never asked for a password.

Obviously we are locked out because I can not troubleshoot his USER settings from control panel.

Any ideas how to recover from this situation?

I am thinking of getting his data out and format it? But can I access the hard disk without the admin’s password?

Thank you in advance.