When I click on "Edit Item" now, I get the editor and all of the features, but the editor no longer appears in a "pop-up" window/layer. I can make changes as usual, and save, but saving no longer dismisses the window and clicking "cancel" has no effect. How did I break this? Or rather, how do I fix this?-Omar

Set your screen resolution to high or higher than you have now and check the editor and see if you can see the x

Have you ever had this working on your site?
If yes, then I would also consider if you have added any plugins running js or jquery that might be conflicting.

Simon
K2 Support

This problem has been fixed... it wasn't really a problem... the K2 system had been disabled from within my Joomla Back-end. But thanks for the responses.