It's possible that some custom files were leftover in the game folder after you uninstalled/reinstalled. Check the folder to make sure it's clean before you reinstall next time.
You can also get the original files back by verifying the integrity of the game cache (rick click the game > properties > local files tab). It check the game's files and redownload any that are missing or don't match up with the default files. Better than redownloading the whole game.