I have a 2600K and Nvidia 570 SLI and I had the game running fine when the last patch came out. I even updated my mod. However, I just tried to run the game and I get the DX9/DX11 selection screen, but nothing happens after that with either selection.
Steam updated something when I ran it and I installed Win 7 x64 updates this morning. Everything else runs fine.
Edit: I ran the Steam Cache verification and now the game starts.