What Happened To Disqus?
Did you add the disqusapi library to /sites/all/libraries (or a similar location)? This happened to my site. Our Disqus comment block stopped loading on existing nodes, and I could not turn on Disqus comments for new nodes.

Then I noticed the message in the Disqus config (/admin/config/services/disqus) that I needed to have the Libraries module installed and api files.

Once I added those files, the Disqus block loaded again.