The 500 Internal Server error is not always due to WordPress. It can be caused by other issues on the server as well. This article addresses the common causes of the 500 Internal Server errors associated with WordPress.

Corrupt .htaccess File

Create a New .htaccess File

From cPanel:

1. In the Files section, click on the File Manager icon.
2. Check the box for Document Root for and select the domain name you wish to access from the drop-down menu.
3. Make sure "Show Hidden Files (dotfiles)" is checked.
4. Click Go. The File Manager will open in a new tab or window.
5. Look for the .htaccess file in the list of files. You may need to scroll to find it.
6. Right click on the .htaccess file >Rename it .htaccess.bak. Alternatively, you can click on the icon for the .htaccess file and then click on the Rename icon at the top of the page.

From the left-hand navigation menu in WordPress:

1. Click on Settings > Permalinks.
2. Review settings to be sure they are set up properly.
3. Click the Save Settings button.
4. Try reloading the site to see if the 500 Internal Server error has been resolved.

Still Getting a 500 Internal Server Error?

Increase PHP Memory Limit

If the error persists, try Increasing the PHP memory limit. Please refer to this article for more information on resolving the PHP Memory Limit Error.

Deactivate/Reactivate All Plugins

If increasing the PHP memory limit does not resolve the 500 Internal Server error, it may be an issue caused by one or more of the plugins installed on WordPress.  Often times, if a new theme is installed, a previously installed plugin will not be compatible and will result in the 500 Internal Server error.

From cPanel:

1. Log into cPanel.
2. In the Files section, click on the File Manager icon.
3. Select Web Root (public_html/www) and the Document Root for the domain using the WordPress install, then click Go.
4. Click to expand the public_html folder, and navigate to the /wp-content/plugins folder.
5. Right click on the /wp-content/plugins folder and rename it plugins.old. This will deactivate all of the plugins. In most cases, this will also lock the WordPress admin area as well.  You will still be able to perform these steps from within the File Manager.
6. Reactivate the plugins folder by following the above instructions and renaming the folder plugins. This will allow you to reactivate each plugin individually to isolate the offending plugin and resolve the 500 Internal Server Error.  This should also allow access to the WordPress Dashboard again.

From the WordPress Dashboard:

1. Reactivate each plugin (one at a time) and refresh the website to see if the issue has been resolved.