Plugins tab won't open at all in WP admin

Well, this is probably a conflict/error being caused by a plugin. Since you can’t access the plugin admin page, you will need to log into your site files to deactivate the plugins. You can do this through FTP or via your hosting account file manager.

Here are instructions for manually resetting your plugins (no Dashboard access required). If that resolves the issue, go back to the plugins page in the dashboard and reactivate each one individually until you find the cause.