OK, I did the deed. Cracked open the case, broke all of the warranty will be void stickers and checked the hard drive to board ribbon cable. It looks fine -- even locked onto the drive with a bead of silicone sealant. Put it all back together and now IT WORKS.

The Engineer in me always wants to know why? All I can tell myself is that maybe we had a loose connection in the ribbon or connector. Hopefully this problem will not show itself in later use!

Anyway, thanks to all who responded so promptly!

Jim