To shut off all comments/trackbacks/pingbacks in the WordPress Admin, the steps for cleanup are:
- remove all pending comments marked as spam (the WP Optimize plugin is great for this)
- disable all comments/trackbacks/pingbacks in the WP Admin (following all the steps here: http://premium.wpmudev.org/blog/wordpress-comments-off/)
- remove all Theme references to
comments_template
/pingback_url
in the active Theme - set archive posts/etc. to disable comments/trackbacks in the database: http://codex.wordpress.org/Combating_Comment_Spam/FAQ#I_have_disabled_comments.2C_but_comments_continue_to_be_posted
- [OPTIONAL] add Theme code to disable comments and access to comments: http://www.dfactory.eu/wordpress-how-to/turn-off-disable-comments/
- Deactive/remove antispam plugins after all steps are completed above. No plugins should be needed if you followed the steps above, but if you need to install a free plugin, [Antispam Bee](http://wordpress.org/support/plugin/