Eu não tenho o Win8 disponível, então não posso dizer que isso funcionará com certeza, mas no Win7 você pode alterar sua senha no prompt de comando. Detalhes completos são aqui , mas as partes relevantes são
To change a user's password at the command prompt, log on as an administrator and type:
net user user_name * /domain
When you are prompted to type a password for the user, type the new password, not the existing password. After you type the new password, the system prompts you to retype the password to confirm. The password is now changed.
Alternatively, you can type the following command:
net user user_name new_password