Archive Pages only showing titles. Used to show excerpts

Hi there

The only thing that I can recall changing on my site is a recent upgrade to WordPress 3.5.

In my /blog page, it used to show all my blog post titles, and an automatically created excerpt.

I noticed tonight that whenever I went to /blog, /category/blog, or /tag/whatever, I got a “No Results Found” page.

I went and pressed the update the permalinks button, and I got a slightly better result. Now I can see the titles, but not the excerpt content. I also see a social sharing bar under every title, and the readmore button. So it does seem as if it is trying to pull content for each title.

Any ideas where to start looking for an answer for this?

Thank you
Brett