Don Cooper wrote:

This same thing happened to me this morning. A first for me as well, and
I've owned Macs since 1995.

I wish I'd had a little more patience, because after a while, I
initialized the HD, some of which hadn't been backed up.

I should have waited and tried other things first.

You can always (for some value of "always") boot from your OS install
CD, backup your stuff while running from it, and then rinse, wipe, and
reinstall.

Most of my Macs have more than one partition or drive housing a bootable
OS, so I can usually get around a boot failure on the primary drive by
aiming it at one of the others.

--
ha