I updated from 3.4.1 to 3.4.2 yesterday and started modifying the theme layout. I added a fullscreen background slideshow, and edited the layout a little more. However, a few minutes after that, my site stopped working, it just kept loading and loading, without rendering anything. I tought it was some script I had added, but I didn't find anything. The site started working again, but it looks like this:

I think it went like this after I removed the background image from the site, but adding it again didn't work. I also tried switching theme, but the width is still broken. It should be 960px wide, but it's only about 600px wide. What did I do, and how do I fix it?
EDIT I know it can't be the style.css file, as changing theme didn't work.
