Restart your computer before trying to reinstall. I don't think this is related to anti-virus, I'm guessing that you just tried to reinstall OBS but game capture's hook DLL got stuck in another process, preventing you from being able to reinstall. Restarting is the most easy way to clear out game capture from anything. (Though honestly game capture should really only be injected in to games, not in to other applications, but people sometimes accidentally inject it in to things like windows explorer or their web browser)