How not to do

Install brand new Windows 7 operating system
In installation process create a new user instead of default administrator account
Authorize with this newly created user (this account also have all administrative rights)
Now you think "Why do i need two users accounts on this computer? I only need one and let it be the default administrator account"
So you choose "manage computer" and set new password to default administrator account.
And now you delete old account. It is very interesting that in user management you can delete yourself when you are already logged in :o
Choose log off
Type new credentials - administrator and your password
A popup came out "Account is disabled. Contact administrator"