Enabling Administrator Account In Windows 7

To enable the hidden administrator account, log into a normal admin account and open a DOS window in administrator mode.

Type in: net use administrator /active:yes

To disable the account, type in: net use administrator /active:no

Check this link for more information:

http://www.howtogeek.com/howto/windows-vista/enable-the-hidden-administrator-account-on-windows-vista/