Microsoft disabled the Administrator account in Windows 7 by default for security reasons.
It is nice to have this enabled as a backup if your main user profile becomes corrupted or infected.
Here is ow to turn on the hidden Administrator account.
There are a few ways to enable this account but the fastest seems to be to open a command prompt with higher privileges by RIGHT-clicking on the Command Prompt menu option (in the windows start menu area) and choosing Run As Administrator.
Once the black command prompt window is open type this and hit enter:
net user administrator /active:yes
It will look like this when you type it out:
C:\>net user administrator /active:yes
That’s it. Now the Administrator account should also show on the Windows 7 log in screen.