How to get back-to-work with a Windows 7 PC that has no admin account?

I have a PC which doesn't have the Administrator account active and the only user account left is a Guest user. I want to get back the admin account but I don't know how to do that with a guest user.

I have tried searching the internet and try to use the Recovery Mode but adding/activating the admin account from DOS not working for me at all. Please help if you meet & solve it before!

Thank you,

Nam.

ps. You can see my diigo try on solving this problem.

http://www.sevenforums.com/tutorials/102552-built-administrator-enable-winre.html

If you follow the steps provided at the above link - you should be able to enable your built-in administrator account.

If that doesn't work then you can reset the built-in administrator or the administrator which is already on there (you would need to know there user name) password via : http://4sysops.com/archives/forgot-the-administrator-password-the-sticky-keys-trick/