Before that, The easiest way to enable or disable the Windows 7 build in administrator account is from the command line. Open a command prompt with administrator rights. This is done by right-clicking on the command prompt icon in the Windows 7 start menu and selecting Run as Administrator from the available options. To enable the Windows 7 administrator account:

net user administrator /active:yes
To disable the Windows 7 administrator account:
net user administrator /active:no
To change the password of the Windows 7 administrator account:
Net user administrator password

An alternative would be to enable or disable the Windows 7 administrator account using the Local Security Policy option. You can open the Local Security Policy by launching secpol.msc from the run box.

Please note that you have only access to the Local Security Policy on certain editions of the Windows operating system. The configuration tool is only available under Windows 7 Professional, Windows 7 Ultimate and Enterprise.

You find the option under Local Policies-> Security Options. Just change the setting Accounts: Administrator account by double-clicking the entry.

This security setting determines whether a different account name is associated with the security identifier (SID) for the account Administrator. Renaming the well-known Administrator account makes it slightly more difficult for unauthorized persons to guess this privileged user name and password combination.

Again, it is not really necessary to enable the administrator account, as it is possible to use a standard account with elevated rights for the same configuration options that an administrator’s account would offer. And it is better for security to not run an administrator account by default.