I've seen the same issue reported other places, but not the exact same issue on this forum.
Game goes to black screen and hangs after starting 400 days DLC, after completion of the main game.
I downloaded the main game from Steam, and the DLC from Steam a few weeks later. Running on Win7 32 bit. So far I've tried verifying the cache (no errors found), uninstalling and reinstalling through Steam, and changing the screen settings to use windowed and a lower resolution.
Support data: http://wikisend.com/download/280230/support_data_pc.zip