Kor
(@korchung)
Hello,
Did you change anything recently? “Error establishing a database connection” usually means there is no connection between your Website and the server database. Sometimes, it is caused by your hosting provider performing maintenance.
You may try fix it by following this guide http://codex.wordpress.org/Common_WordPress_Errors#Error_Establishing_Database_Connection
Regards
KC
There is a problem between connection with your website and its database. It can be wrong database credentials in wp-config.php file, crashed database, missing database or some other error in wp-config.php file.
For more information you can read this detailed guide: https://colorlib.com/wp/fix-error-establishing-database-connection-wordpress/
If nothing from above helps, make sure to contact your hosting provider as they might have more information about this problem.