Thanks for your ideas - fortunately, I don't think it's as bad as all that. We can actually run the PC, and the lightning detector, and it seems to work. (Only tested it with a gas-lighter, because there's no lightning around just now.) What we can't do is boot up with the StormTracker card installed. So until we find a real solution, we'll just have to uninstall it whenever we reboot - which is messy, but better than nothing.