Twine 2.1.0 starts but won't accept commands, including Quit

I recently updated to Twine 2.1.0 on Windows 10 64-bit. When I start the program I get the menus but an otherwise blank window - no "Create new story" or anything else. When I try to use the menu commands nothing happens, including when I use them to try to quit. Same thing with shutting the program down via the X or Alt+F4 - nothing happens. The only way to shut it down is via the task manager.

At first I thought the problem was that I had installed it in a non-default library, but I get the same issue when using the default.