After installing Visual Studio 2012, I found that the open file dialog wasn’t being displayed. I could open projects via Windows explorer, via the recent projects menu, compile, run etc, however neither Open Project or the File->Open->Project/Solution were working.
What was strange about this is that other dialogs such as New Project were working fine.
After much searching and testing, enabling the Tablet PC Input Service fixed the issue. This does not make much sense since I’m not using a tablet pc, however it works for me and may work for you.
To enable the service: