Back UP, Sites and WP gone down

Followed WP instructions to back up my database via phpMyAdmin. Exported back up files fine. BUT now no websites. Can’t log onto WP Admin. . . “WP Error establishing a database connection”. Username&Password correct unless it automatically reverts to something else. Hostname correct. Database server is up and running. Where can I find out if WP is still installed. Database still intact, passwords all ok. wp-siteurl ok. wp-config.php empty. . . any idea’s or check list of things I should check ?? THanks