OMG! Someone changed the super user password and now nobody knows how to access the site!
(ugh!, there was a single super user account created on the DNN instance)
OMG! I've restored (with DNNBackup, of course) this site, but I don't know any user I can use to login!
OMG! The user is not configured to allow new user registrations, and anyway I don't have direct access to the database to make the 'issuperuser=true' trick!
Don't worry, download this "LetMeIn.aspx" page and upload it to the root of your web site. Then execute it by calling it in the browser (http://www.example.com/LetMeIn.aspx). You'll get a simple form like seen in the screenshot below. Create a new host (super)user and you'll be able to access your site.
Remember to delete "LetMeIn.aspx" as soon as you've finished!