define ('WP_HOME', 'http://localhost/wordpress-folder-name' );
define ('WP_SITEURL', 'http://localhost/wordpress-folder-name' );

For my part, it was different from the other answers. My database was set correctly to http://localhost but I had a plugin installed to manage SSL (Really Simple SSL).

So I renamed the folder /wp-content/plugins/really-simple-ssl to something different and it worked.

And to access /wp-admin without SSL, you need to change your /wp-config.php file and set FORCE_SSL_ADMIN to false.