Thanks - I wondered if it might be something like that. Never messed with the BIOS before either, but there must be plenty of good directions on the Web. Will try it tomorrow when a big backup task has finished.
Seems odd in one way, though: the new drive contains (I hope) a full image of the original HD. Shouldn't that be bootable too? Or maybe I'd have to insert the Acronis CD, or the new recovery disc it made for me, to open the backup file.
Thanks to JN too. Could that "teach" the Vaio which is the right boot drive in a way that it will remember, or do I need to go into BIOS anyway?
BTW, the tech who revived my computer after the original boot-sector crash had said that SATA drives are hot-swappable, or I'd never have tried. I was always taught never to plug or unplug equipment with power on.
Much obliged for the good advice-