I faced that problem few months back. what i did is reformat my pc. but there is one more way is to create a user from control panel and give that user administartor access. Try it more...
Microsoft Windows XP Professional for PC - Troubleshooting
Do you use administrator account? if you use another account then try this: try just leave blank the password and press enter. username: administrator password: ____________ press "enter" in the keyboard. If your can in this account then you can change your password in the control panel. more...
Microsoft Windows XP Professional for PC - Troubleshooting