This either means that the username and password information in your wp-config.php file is incorrect or that contact with the database server at sql311.byetcluster.com could not be established. This could mean your host’s database server is down.
If you log into your InfinityFree account and click on your account name then go to Databases you should see your database connection info listed. You can also try to go to Control Panel and click on phpMyAdmin to try to connect to your database. Try those methods first to see if you can connect. Then you can troubleshoot the WordPress issue later.