Error Establishing Database Connection!

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?

I’ve read the comments regarding possible problems during an install, but I haven’t seen anything on why this might happen with an install that’s been running properly for months. I haven’t modified anything since the install.
Any help you can provide is appreciated.
-John