Can’t edit existing posts

All of a sudden, I can’t edit existing posts anymore. I can create new posts, edit categories, but I cannot make any changes to old posts.

When I go through my wp-admin and click on edit posts, I see a blank grey space where the list of posts is supposed to be. Here’s a screen grab.

When I click on “edit” underneath a post, it takes me to a screen that looks like this.

Any ideas? The only recent changes I made was upgrading Firefox to 3.5. My website is http://www.publicmediaservice.org in case there is something you can see in any page source.

I am also unable to do the automatic upgrade to 2.8. When I try it hangs at the downloading .zip stage. Thought I’d mention that in case it’s a clue.

Thanks,
Andy Cahn