I'd try playing with the config settings first, if you haven't tried to already. Settings in there sometimes cause problems in conjunction with Windower (nothing game-breaking in my case, but that's my best guess if it's crashing on start) and maybe it's confusing things even when you're running without. Since there's more than one of you, messaging them and seeing if there are similarities between your installations might cast a light on what's broken.
But since a corrupted install seems really likely and file check isn't catching it, your final option is to reinstall. Or alternatively, root through every one of the four thousand files that changed via the update you extracted (because presumably this was the action that broke things), and then somehow magically figure out which one or ones became a problem. You can do it!
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