How to fix Link to database cannot be established error

in ,  
Problems
"Link to database cannot be established."

Solutions

This error happen when you have wrong database information in the prestashop settings, so it not connected to the database sever.
So browse to your files with ftp client or true Cpanel if you have and go to the following folder, /public_html/config/ then open this file settings.inc.php
You see this info there,
define('_DB_NAME_', 'your_database_name');
define('_DB_SERVER_', 'localhost');
define('_DB_USER_', 'your_database_username');
define('_DB_PASSWD_', 'your_password');
Make sure all above input are corrected.