I just killed and restarted VS a couple times because I thought VA deadlocked or something when I opened the snippet dialog. Turns out I just couldn't see the (modal!) dialog. When I hit Win+<Left Arrow> the dialog would toggle between left half of the screen, right half, and invisible. Anyways, invisible modal dialogs are evil.
I recently stopped using my second monitor. I probably had the dialog on the second display. Might be a Windows 7 bug though.