Well I had the same problem few months back. "Verify Integrity of Game Cache" & reinstall didn't help - I thought that I'm stupid or will I need to reinstall even W7 to make it work.
Answer is simple. Run Steam as a Administrator (Steam shortcut> Properties> Advanced> Run as admin ) and that's it.
Answer is simple. Run Steam as a Administrator (Steam shortcut> Properties> Advanced> Run as admin ) and that's it.


