Error establishing a database connection

I can not access my blog.
This is error:
This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at hostingmysql326.register.it. This could mean your host’s database server is down.

Are you sure you have the correct username and password?
Are you sure that you have typed the correct hostname?
Are you sure that the database server is running?

if I try the backup installation,this is fhe errore:

Access denied for user ’81b0de652_ece5f3’@’172.20.81.1′ (using password: YES)