Media uploader not working

When I am on a page or post and click the “Add Media” button, nothing happens.

If I click “Set Feature Image” the media browser replaces the entire page instead of being a lightbox popup.

I have tried disabling all of the plugins, but that didn’t help. I am a bit scared of switching themes to twenty-eleven because this is my friends site and I don’t want to mess it up.

Any ideas? Thanks