Boot the PC in Safe Mode by pressing the F8 key.
* Select the Safe Mode option, now you can now Login as an Administrator and XP won't prompt for the Password.
* Try rebooting the PC in DOS.
* Now, Access to C:\Windows\system32\config\SAM.
* Rename SAM as SAM.mj.
* Now XP won't ask for Password next time you Login.
* Now, again go to Start menu --> Run.
* Type there cmd prompt.
* Type net user *, It will list all the users.
* Again type net user "administrator" or the name of the administrator "name" *. * It will ask for the password. Type the password and there you are done.
* Hold the Ctrl+Alt key and press Del twice. This will bring up the normal login and you can log on as Administrator. To unhide the Administrator account so it does show up.
* Again go to Start --> Run --> regedit.
* Go to HKEY_LOCAL_MACHINE --> SOFTWARE --> Microsoft --> Windows NT --> CurrentVersion --> Winlogon --> SpecialAccounts --> UserList.
* Unhide the Administrator key by giving it a value of 1.