Have you tried:
– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the Twenty Eleven theme to rule out any theme-specific problems.
– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.
– re-uploading all files & folders – except the wp-content folder – from a fresh download of WordPress.
I too had the same exact problem after upgrading yesterday (6/13/12). Could not change the columns, and also in the Themes section, it would show two themes screenshots, and would not let me view live preview. I also noticed that if I changed to default 2011 theme, everything looked normal. This led me to my theme, which I use Graphene plus a child theme.
So I deactivated the child theme, and used the parent Graphene theme, and things still looked “normal”. This led me to the child theme.
I backed it up (only had style.css and a couple changes in the functions.php file) and created a new child theme. Activated it, things were still normal.
So one by one I uploaded my old child theme files until I found the culprit which was the functions.php file.
I had two options in there. 1. Remove admin tool bar for non-amins, and 2. Remove the query after all scripts. (ex. http://website.com/pic.jpg?ignore=this-query-string)
I had to remove the query customization and now everything looks normal, using my child theme. I will have to find a workaround for this because all my caching is wrapped around the no query.
I would suggest testing your theme files as the Theme Diva suggested!
