404 error when i visit /wp-admin/options-discussion.php

Hello, I wanted to disable moderation of comments so i clicked options then Discussion which took me to page /wp-admin/options-discussion.php. But it gave 404 Error: Not found . Full url is http://lawlex.co.cc/wp-admin/options-discussion.php . While i checked this file on File Manager Client, it is present there in wp-admin .Im having granted full access to this file. I have tried reinstalling options-discussion.php file and also whole wordpress. But problem is still there unresolved. All other options are working fine. Kindly help me with full instructions. Thanks. PS – this function was working fine 2-3 days ago.