What causes a database connection error?

Question

MySQL

Hosting nic.ru uploaded two sites to WordPress. I bought another domain for the site, decided to connect WP through hosting, updated the database and the password in the database, both sites crashed, when displaying sites in the browser, it says: "Error establishing a connection to the database", wordpress is not installed, changed the password in wp_config, not helps.
I can provide screenshots.

Help solve the problem!

Answer 1

Well, umm... the trick is that.. umm.. database connection error, most likely! Due to the fact that there is no access to the database, or the data entered is not the same. Or you write something clumsily when setting up.