Happily I can say I am now typing this from the computer we "were" working on. Unfortunately your "So others (and I) can learn...
" in your sig will not benefit. I have no Idea what I did to get her back from the dead. All I did do was delve back into BIOS, open and view all the pertinent parameters (no changes made), close and save. Upon the next reboot it opened smoothly all the way to Windows 7. I took a moment to revert back to my restore point and then physically checked the reg was back to normal (which it is) so for now all is well. Think I'll just skip AHCI for now.
The thing I really wanted to check was hard disk boot priority in BIOS (which was OK) because the boot screen has always displayed my primary OS drive as being attached to IDE Channel 2 Master. On IDE Channels 0 & 1 (master and slave) only the Slave 0 is being utilized and this is by a PATA drive. Not sure it really matters but that is for a different thread anyhow.
Thanks again for your support!