OT: system shuts off sporadically

[Vaughn Treude]

One more report - if everybody isn't totally bored with my hardware
problems.  :-)
The machine was up for exactly 99 hours and then it locked up hard. 
I've experienced this 3-4 times before.  It's always been when I've been
using the CD player, usually when changing CD's.  It hadn't  happened
since I upgraded to a later version of the earlier, buggy version of the
CD player that came with Ubuntu.  Oddly enough, the machine wouldn't
boot after this, would turn on but nothing would happen.  I had to
actually switch the supply off and then on, and then it worked.  So
there was some bad hardware condition that was being preserved with the
machine in its powered-off-but-network-card-is-powered-on state. 
Weird!  Just out of curiousity, has anyone else experience this
problem?  I'm using an Abit motherboard.  The problem must be related to
the on-board sound chips because it's occurred with both CD drives - one
which is IDE, the other SCSI.
Vaughn