I have no idea what happened, maybe a kernel panic. Last night doing a spotlight search (on intel imac cd) and the screen went blue.
I was able to reboot but after starting Onyx I got the message that the start-up volume needed to be repaired
I ran disk utility from install cd to do a repair disk but it would not complete. Got the following message each time I tried -- "The underlying task reported failure on exit."
I bought and downloaded Diskwarrior on my ibook. I started the imac in target disk mode and ran Diskwarrior. It rebuilt my directories and NO MORE PROBS.
$100 is pricey but well worth it. I had visions of having to do an erase and install.
BTW I was also fully backed up on my external and this lessened the anxiety of this experience.