Command Prompt on Logon Screen
For XP User
Go to C:/windows-system32 Copy cmd.exe on your desktop
Rename it to sethc.exe. Now copy that file and paste again in system32 directory. When windows ask for overwriting the file, then click yes.
Now Log out from your guest account and at the user select window, press shift key 5 times or Left (ALT+Shift+ Num Lock).
For Windows 7 User
Right click on sethc.exe and run as administrator.
Right click on sethc.exe, Click on properties. and Click on Advanced tab
Now Select your Current user and click on Change Permissions
Now Click on Edit
Now Click on Full Control Check Box and Click OK
Copy the New sethc.exe to system32, and click copy and replace
Now Restart your PC
Resetting the Password
Once you get to the login screen, hit the Shift key 5 times, and you’ll see an administrator mode command prompt.
Now to reset the password—just type the following command, replacing the username and password with the combination you want:
Command : net user account.name *
Example: net user raaz *
and hit enter. Set any password for that account