Here is one way to troubleshoot and fix your Joomla site when it is showing only ~Error~ on the 500 server error white screen of death.
The required fix here was updating this site's Rockettheme Template to the latest available solution.
The steps to do so also apply to other out of date Joomla templates causing issues.
Remember to backup your site first!
Here are the links mentioned in this Live Stream:
Enter to Win ► https://www.basicjoomla.com/giveaways
Backing Up Your Joomla Site with Akeeba ►