First off if this is in the wrong section please move it or tell me. Anyway, I broke my sound.lua, can someone tell me how I can get it back or give me a new copy?
Delete it then do this: From the Library section, right-click on the game and select Properties from the menu. Select the Local files tab and click the Verify integrity of game cache... button. Steam will verify the game's files - this process may take several minutes. Once the process is completed, the Check Window will automatically exit.