Hi,
my site shows a 500 error: Internal Server Error
It reads only html files. Even if I put only one index.php file with the "<?php echo 123; ?>" into the "public_html" and nothing else - it can't read it.
Learn the reason from error logs. It seems to me you're using mod_suphp, and it's permissions issue. PHP scripts should belong to user:user, 640/644 (not more) and directory user:user 750/755 (not more).