Error in establishing a database connection

hello dear fellows,

have a wp running on a dedicated server…

i still get the error:
Error establishing database connection

belive it or not:
Errors remain the same - even if i follow this workout:

…/wp_allow_repair-repair-optimize-wordpress-database/

The WP_ALLOW_REPAIR constant, when used, activates the native WordPress feature to repair corrupted tables in the database. The same feature can also be used to, in addition to repair, optimize tables.

If you are a seasoned professional, with advanced knowledge, prefer the use of tools for database management, or the unshakable terminal.

Using the WP_ALLOW_REPAIR constant
This constant must be placed in the wp-config.php file. Its value must be a true boolean. Like this:
define (‘WP_ALLOW_REPAIR’, true);Once you have added this setting to the file and obviously saved it, access the following URL:

/wp-admin/maint/repair.php

WP will display the following interface:

A simple and explanatory interface with two alternatives: repair the database or repair and optimize the database. The difference between the two is that in the second alternative an optimization will be performed after the repair.

well i guess that the mysql-server does not work at all