I'm on a Mac but I've had similar problems. Usually it happens when Bryce is either running out of memory or if the processor is really thinking about something. Things that help to avoid this problem in my experience is setting the preview window to wire frame. Buidling things in solo mode. So if you have a really complex project, click on the somehting you want to build your next thing by or near and then go to solo mode. That way Bryce doesn't have to show you where the rest of the complex stuff is--just what you're working on.