other than deny access to everyone, including the owner.

Creating an account in OS X without a password is not a good idea. The password is there for a reason and helps prevent what you were trying to prevent when all this went south.

Let's try this.
Boot your MacBook from the OS X installation disk, or the disk that came with the computer, and as soon as the text appears in the menu bar, choose Password Reset. It's probably under Utilities.
Reset all the passwords to something, anything, just not blank.
On completion, reboot and log on.