The Pspasswd tool, which is part of the Sysinternals PsTools download, can be used to reset the local administrator password across one or more machines locally or remotely.

The tool must be run while logged on with an account that has administrative rights on the target computer, for example a domain admin account. You can also specify those credentials via the command-line. Pspasswd uses Windows authentication methods to authenticate to remote systems and does not put passwords in clear text over the network.

For a single computer:

pspasswd \\computer_name Local_administrator_account_name “New_Password”

For multiple computers:

pspasswd \\computer1_name,computer2_name,computer3_name Local_administrator_account_name “New_Password”

For all computers in the environment:

pspasswd \\* Local_administrator_account_name “New_Password”

For multiple computers using a text file containing the computer names:

pspasswd \\@file.txt Local_administrator_account_name “New_Password”

 DEMO:

How it Works on Windows 7 - in Video (Portuguese Brazil)