The next step to take if you are troubleshooting an issue with a database backend is to see if you can connect correctly. This usually means checking the files that your site reads to find out the database information.
For instance, for a WordPress site, the database connection settings are stored in a file called¬†wp-config.php. You need to check that the¬†DB_NAME,¬†DB_USER, and¬†DB_PASSWORD¬†are correct in order for your site to connect to the database.
You can test whether the file has the correct information by trying to connect to the database manually using something like:
mysql -u DB_USER_value -pDB_PASSWORD_value DB_NAME_value
If you cannot connect using the values you found in the file, you may need to create the correct accounts and databases or modify the access permissions of your databases.