My website is not functioning at all

Website- https://www.bonfirememories.com
When accessing the site, I get an “error 500” in IE / and nothing in Firefox! I cannot login or get the login page using /wp-admin or /wp-login.php. Following another post, I uploaded a “hello.php” file to my server with <php info in the contents, and it worked.

It must be the WP files. I’ve installed and re-installed files, and checked my config file.

I was installing “delete-revisions” plugin and added define(‘WP_POST_REVISIONS’, false); to my .htaccess file, which completely worked with two other of my sites with WP.
The symptoms of this site did not allow me to log out. No my site is gone! Please help me.