Blank screen on iPhoto 11 - no thumbnails, no outlines of thumbnails, just blank

I cannot see my thumbnails in iPhoto 11 (v.9.4.2). I am not getting blank outlines or anything indicating there are any photos, just a blank screen - see below. The screen is similarly blank but white when I try to access it from the Finder. If I click randomly and drag, a transparent thumbnail of that photo appears, so there seems to be some connection to the images, they are just not displaying. I have not touched the iPhoto library or done anything with my computer - the images were appearing an hour ago. My PhotoStream still appears to work on my iPhone and my other computer, if that means anything.

Thanks in advance for any help!