I get this error when my site tries to load

I’ve been getting this error today several times when trying to access my weblog.
Any idea why???
“Error establishing a database connection! This probably means that the connection information in your wp-config.php file is incorrect. Double check it and try again.
* Are you sure you have the correct user/password?
* Are you sure that you have typed the correct hostname?
* Are you sure that the database server is running?”
Thanks ??