UPDATE - took it back and the lady in the store showed my how she had installed the bobbin case incorrectly that morning. Then (thanks Prism, good suggestion!) she plugged it in and we did some sewing.
It worked.
I now know how to remove and reinstall the bobbin case correctly, thanks to their having done it wrong twice. I shudder to think of what else they might teach me to do wrong, so I am going to download the real manual (not the happy little user guide) that came with the machine and learn to do it right.
When I get this scrappy quilt done, it will have more than one meaning of "scrappy" associated with it!!!