Just log onto the Adminstrator account. If its files were deleted they will
be recreated.
When you arrive at the Welcome screen hit CTRL + ALT + DEL twice in quick
succession. A box opens.
Enter:
Administrator
as the user name and whatever the admin password is as the password and then
log on as the Administrator. You can create new Adminstrators-level accounts
from there or elevate any current accounts to Administrators status.
If you can't get into the Adminstrator account via the CTRL-ALT-DEL at the
Welcome screen, reboot the computer, use F8 to boot into "Safe Mode with
Networking", log in as Administrator and fix up the accounts that way. If
the files for the Administrator account are gone they will be recreated.