What you have to do if you log out from the site without enabling an Account login module

The site is configured with a copy of the login page which displays the Account Login module. The administrator cannot edit this page, but an alternate page can be checked and set as default login page. In order to introduce such a modification, when logged in as an administrator, check the option “Site settings”  in the Menu or click the icon . Click Advanced settings and Other settings.

If you log out from the site without enabling an Account login module visible to all the users you cannot login any more. If this should happen, you need to access the page  nuke.domainname.xxx/emergencylogin.aspx

This will display the default login page.