Sorry for being out for a few days, and mighty big thanks to everyone for the suggestions. I did manage to fix the problem, and this is weird, but I remembered that I had run TweakNow RegCleaner since the last time I used Biab, so, I rolled back W7 to the day before I did that, and Lo! I was able to get back up and running.

Have no idea why, as I don't recall any messages about Biab or anything else during the process, but there it is, I'm up and running!

Think I'll do lots of restore points in the future...