Oh it wasn't actually a bug like I thought- for some reason the game simply switched the audio settings to no sound after I finished one mission and started the next; the music setting remained normal, but the sound went off. After the trouble I had getting the thing to start and reading about so many troubles here, I thought it was a real bug- until I thought of the simple solution that turned out to be it. I guess it is a real bug that turned the sound off, but it's simple enough to just reset it. But I'd already started the thread and couldn't delete it
