The second method is much faster. To set the Administrator’s password via the Command Prompt follow these steps:

Click Start and type CMD. 
Press CTRL+SHIFT+ENTER to open the command Prompt with Administrative rights. 
You can also right-click the CMD icon and select “Run as Administrator”.


  
If you have UAC enabled (read my “Disable User Account Control in Windows Vista” article) then you will be prompted to accept the action. 
At the prompt in the Administrator: Command Prompt window, type the following command, and then press ENTER:

Net user administrator myPa$$w0rd12 
Note: The above action will set the Administrator’s password to “myPa$$w0rd12”, you may select any password you want.

Step 2 – Activating the Administrator’s account
To activate the Administrator’s password follow these steps:

Click Start and type CMD. 
Press CTRL+SHIFT+ENTER to open the command Prompt with Administrative rights. 
You can also right-click the CMD icon and select “Run as Administrator”. 
If you have UAC enabled you will be prompted to accept the action. 
At the prompt in the Administrator: Command Prompt window, type the following command, and then press ENTER:

Net user administrator /active:yes 
Log off of your user account and you will see the Administrator account on the Welcome screen.



You can now logon as the default Administrator account.

Note that now you can also view this account in Control Panel.