Hard lockups of a system which has been in operation since mid-2003 are never fun, especially if it's your main workstation!  I even went to my (Linux PC) router, and attempted a ping, hoping I could log in remotely and shut it down cleanly.  No such luck.  I had to hold the power button for an extended time.

What was even worse and more heart-pounding was that when it went through the end of POST and was about to load GrUB was that it froze.  I thought the mainboard, the EIDE/SATA subsystem, or my hard disk had bought the farm.  I frantically ejected the CD/DVD tray, which had a CDDA disc in it (which has been known to mess with boot, because it'll look for a LONG time for something El Torito), except that wasn't any help.  Ultimately, it was some attached USB mass-storage class devices which did not have a working boot sector which was the cause of my panic.  It's fine now; I'm typing this post on the very same 'puter.
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