A majority of the times I have experienced something like this its been
heat related.  I had one just this week that was a dead CPU fan.  If
there was nothing obviously wrong then you can try things like memtest86
(I think recent Ubuntu versions install this as a grub option by
default, mine says "Ubuntu, memtest86+").  Errors during memory testing
can mean either bad memory or heat problems.

Could definitely be bad mobo, ram or cpu.  Craig mentioned leaky caps.
Abit had some problems with that I think, so definately worth checking.
 Another time I had this problem was when my mobo, cpu, heatsink
combination resulted in a heatsink not properly sitting on the CPU.  I
ended uphaving to get a heatsink that would fit better.

Good luck.

Austin

Vaughn Treude wrote:
> Hello everyone:
> I've been experiencing a problem with one of my PC's.  Eight months ago
> I upgraded it to an Abit VIA KM400A motherboard with an AMD processor
> and new RAM.  In the last couple of weeks it's started shutting itself
> off sporadically, for no apparent or consistent reason.  I know it's not
> a software problem (though if anyone wonders, I've got Ubuntu on it, and
> have been quite happy with that flavor of Linux) because it has at times
> shut itself off while I'm in the BIOS setup screen.  I have replaced the
> power supply and that didn't help.  I suppose it's probably a
> motherboard problem, and I believe it's still under warranty, BUT
> sending it back will be a hassle and I'll lose the use of that machine
> for a few weeks at least. Most odiously, I'll have to reinstall the
> processor and mess with that heat sink junk once again. So I'm wondering
> if anybody knows of anything else that could cause this problem.
> 
> Some more info:
> - The problem appears to be totally random, sometimes happening within a
> minute of startup, sometimes hours later.
> - Sometimes the system will not restart for a few minutes after this
> happens.  Or sometimes it will start but not boot.
> - Often when this happens the BIOS checksum gets corrupted and I have to
> re-enter my settings.
> - In BIOS, I've taken care to turn off features I'm not using, such as
> APIC and SATA support. I've turned off power management to the extent
> the BIOS allowed me to do that. I've also set the power-off switch mode
> to a 4 second delay, in case there could be noise spikes on the power
> switch line.  I've turned off the "halt on errors" feature.
> - In the BIOS PC health screen the CPU temperature appears to be well
> within the good range.  However, I've only checked this shortly after
> power-on.
> - The motherboard is rather compact, and is mounted in a maxi-tower case
> with extra fans.  I don't know for a fact if the airflow is optimal.
> - I've checked the system logs and there is absolutely no record of any
> kind of error at the time it powers itself off.
> 
> Any ideas of what I might try, or any resources I could use?  I googled
> for it under "PC sporadic shut off" but didn't get any useful hits. 
> Half of the problem with googling for a PC problem is knowing what to
> call it!
> 
> Thanks in advance for any suggestions you might have,
> Vaughn
> 
> 
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