If your website is using Joomla CMS and you get errors connecting to the database such as Error displaying the error page: Application Instantiation Error: Could not connect to MySQL, you can try the following steps to fix the problem:
1. Login to your Control Panel and select the File Manager menu.
2. Select and edit the configuration.php file located inside your hosting root folder.
3. In the database settings section, customize the details with the database you have created:
public $db = 'username_dbname';
public $user = 'username_dbuser';
public $password = 'contohpassword';
public $dbprefix = 'jos_';
public $host = 'localhost';
Or have you encountered an error similar to this:
Error displaying the error page: Application Instantiation Error”
Please follow the steps as before by checking the configuration.php file.
If it doesn't work, it could be because your joomla script doesn't match the php hosting version. For example, if your php hosting version is set to 5.4, then you can try to increase the php version to 5.5 or other and check the results.
Good Luck