guys, plain and simple, The golden rule of Steamand all hl mods: When something goes wrong, AND IT WILL:
1. Back up your data, the entire directory
2. Remove the Steam or Mod's directory
3. Reinstall into a Fresh, unused Folder with nothing else there, so if it was "C:\steam" Make it "C:\steam(new)\steam" or something jazzy like that
4. boot your app!
I've heard this even from tech support at Sierra, Just follow that and you'll be set for any issues, cept for Fmod issues :p