If your WordPress site is showing a 500 error and you can’t figure out how to fix it the usual way (disabling plugins or themes, increasing memory, etc) download the most recent copy of WordPress, unzip the wordpress.zip and delete the wp-content folder. Then go to your WordPress folder on the host and remove anything that begins with ‘wp-‘ other than wp-config.php (it contains your database info) and the ‘wp-content’ folder. Then delete index.php, license.txt, readme.html, and xmlrpc.php. Then upload all the remaining files in the unzipped folder.