How did you delete the admin account?
You can only delete it from another admin account, since you cannot delete from a standard or guest user.
Have you tried creating another Administrator account?
Boot into safe mode by pressing F8 at boot time and once in Safe Mode, the built-in administrator account is available automatically (no password by default).
If you deleted the Windows built-in administrator account, and you have no other accounts, then you have to erase the computer and re-install Windows.
If your computer was shipped with Windows 7, then you could use the manufacturer's built-in recovery mode.