Amnesia will not launch from Steam?

[IWork4Dessert]

A few weeks ago, my MacBook Pro suffered from a total system failure. Every game on my Bootcamp side(Windows) was completely wiped out--including Skyrim and Civ V, fml. On my Mac side, I managed to recover all of my files. However, when I launch Steam, none of my games will work. I wouldn't be particularly worried about this except that I'd gotten to the torture room in Amnesia and that took a whole hell of a lot of 15 minute segments of terror to get to.
Sooooo because I'm stupid, I deleted all the local content in an attempt to fix my game. Which was tragic blah blah blah but I thought, hey, at least I'll be able to play. Wrong.

Every time I open Amnesia(from any location, in online or offline mode), there's a little window that says "Preparing to launch Amnesia: The Dark descent..." that appears for about 3 seconds. Then it disappears, it un-focuses my windows as though it were launching the game, and then goes right back to Steam. No error message, nothing. All game files are supposedly intact.

Please help me...