Suddenly receiving "Already Installed" message when trying to log in

When trying to get to log-in page or just opening site, I get this message:

“Already Installed: You appear to have already installed WordPress. To reinstall please clear your old database tables first.”

Even when I type in the url it always jumps to the “install.php”, as in https://mtmcclanahan.com/ThePaintersTongue/wp-admin/install.php.

This apparently happened overnight–was fine the night before and like this the next morning. This is the only site I have running 3.8.1, but as I said, was working fine before.

WordPress 3.8.1; Twentyfourteen theme; https://mtmcclanahan.com/ThePaintersTongue/ or just https://thepainterstongue.com.

Thank you for any help,
Marcus