The dreaded "Error establishing a database connection"

This error message occurs when I try to go to the admin page, and it also pops up when I select specific blog posts.

Here it is, specifically:

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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 localhost. 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 you’re unsure what these terms mean you should probably contact your host.

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The home page, however, comes up OK. It’s at route66news.com. And third-party sites insist the website is up.

The weird part is I haven’t done any tinkering at all since the 4.0 rollout, which it handled fine.

And, yes, I’ve been able to access the cPanel just fine.

I’ve emailed my host, but I suspect the problem isn’t on his end. Suggestions?