Error establishing a database connection

I just installed the plugin and started staging the site, but it crashed the site and I had to stop the copy. Now, when I enter the URL, it says “Error establishing a database connection,” and when I enter /wp-admin, it says the following:

Error establishing a connection to the database.

This means that the username and password information in your wp-config.php file is incorrect or that contact could not be established with the database server at 127.0.0.1:3306. This could mean that your host’s database server is down.

Are you sure you have the correct username and password?

Are you sure you have entered the correct host name?

Are you sure the database server is up and running?

If you are unsure what these terms mean, you should probably contact your host. If you still need help, you can always visit the WordPress support forums.

I need urgent help, please