This post describes how to reset a forgotten Windows 7 administrator password:

First create a Windows 7 installation disc or pen drive. For pen drive, you can use Rufus.

Once you have an installation medium, boot off it. You may need to tweak the bios settings at boot to enable booting from this.

Once installation starts, choose “Repair your computer” option. Get to the command prompt, and execute the following command:

copy c:\windows\system32\sethc.exe c:\
copy c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe

Reboot PC. Start windows, get to the login screen, and press Shift key 5 times to get an admin (elevated permissions) command prompt. Execute the following:

net user myuser newpwd

to change the password for the user “myuser”.

If you dont have an admin user installed, create one now:

net user /add [username] [password]

This creates the user account.

Add the new user to Admin group:

net localgroup administrators [username] /add

As a security precaution (even though Windows is inherently a security risk), always set a bios password to prevent novices from accessing your system internals. Of course, they could always open the chassis, reinsert the battery to disable the bios password. 😉