Rebooted, shut down, reseated cables. BIOS sees it. Device manager does not see it.
Installed this build with the DVD drive, then nothing.
My husband solved this one for me with some intelligent web searching. There are several fixes suggested in Windowsreport by Milan Stanojevic.
He used a really incredible, cool fix:
It seems really drastic--like the kind of thing I would only try if I were really, really angry. But it worked like a dream. Problem solved.