Administrator account got disabled

http://www.pctimelimit.com/how_to_enable_administrator_account_windows_xp.html

If you are logging in at all, it probably is an admin account. Otherwise, try safe mode. If you get in, just re-enable, and skip regedit instructions.

Boot from Windows CD and run the setup, skip first console repair and hit Enter, then setup will detect your Windows installation and ask you to repair it, choose repair.
While Windows repairs, when you reach the GUI interface during Device drivers installation hit (Shift+F10) this will open CMD window, from there you can do whatever you need, like opening user management from the following command "Control userpasswords"
then you can Enable the account, create new one, change passwords, etc...
Good Luck