Comments won't work on Wordpress site

I can't get comments to work on A long time ago my client who has this site asked me to do whatever it takes to stop comments across the whole site. So I used a plug-in that did just that, I think by putting in a permanent fix into the site code. How can I fix it where comments works again? I have turned them on in every way I know how. Please advise. I am running Wordpress 4.5.3 and the Elegant theme Divi version 2.7.8