Plugins won’t activate

Argh, had to fix my last problem by hacking wp-comment-post.php file, it simply would not listen to what I told it about setting Comment Moderation to “none”, it just would not work, so I changed:
wp-comments-post.php:
if(check_comment($author, $email, $url, $comment, $user_ip)) {
$approved = 1;
} else {
$approved = 0;
}
$approved = 1; // added
Now, More trouble this time 🙁
This time plugins just will NOT activate, it says it is activated, but the state does not change, and the plugin will not work, so I assume it is not activated.
I only want to activate the search highlight plugin, but it won’t. Can it be activated by hand? Database setting, or change something in the source file?
I have made sure every wordpress file is writeable, but it still will not activate.
http://robvdl.sitharus.com/test.php