Error establishing a database connection

Hi, I was just to post on my blog another post after one I posted few minutes ago but I got this error:

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Error establishing a database connection
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 (removed host address) This could mean your host’s database server is down.

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My host is up, I have a forum and different websites on the same server and its all working fine.

What can I do?

Thanks