Server is down.

It looks like you can no longer access the database installed with the web server.
Please make sure that the database password, user name, and database hostname set in wp-config.php are correct, as described in the error description.

Also to be specific the error message is looking for the DB on a loopback interface 127.0.0.1:3306

1. I would think your DB is not running local on the WebHead, that is poor practice.
2. That there was some port forwarding that you or someone had done in the past that wasn't made permanent.

Solve this by making sure reachability to the DB is possible, plumb Security Groups, and lastly make sure you php file is updated to the proper IP of the DB in question.

Let me know if you have any issues with this, or if it helps you then please accept my answer after you've tried it out - it would be much appreciated! Good luck :)