Blank Dashboard but front-end loads normally

I just upgraded from 3.21 to 3.3. Upon upgrade, my dashboard immediately went blank, leaving me with no way to add posts, pages, plugins or anything else.

I’ve read through the troubleshooting master list for solutions. Thus far I have tried the following with no success:

Renaming my plugin folder (thereby disabling any plugins)
Forcing WP to use the Twenty Eleven theme by deleting my others via FTP

What else can I do to get this working again? I’m not sure exactly where the problem lies (I’m not using that popup plugin, nor have I ever). I am using a W3 Cache plugin but, again, when I remove all plugins the dashboard still loaded improperly.

Here is an example of how it looks now.

https://farm8.staticflickr.com/7032/6512129675_10cfe54469_z.jpg