[ale] Server PS shuts off for no reason

[hbbs at comcast.net (Jeff Hubbs)]

I have a SuperMicro 5013C-T 1U server that I've been setting up over
many weeks and just recently, it's started shutting itself off after a
period of seconds (i.e., not even long enough to finish booting),
minutes, or even many hours.  The interesting thing about this is that
the power LED on the front panel remains on. 

Are there any non-hardware-failure things I should check?  I can't
correlate these shutoffs to any one thing I might have done, especially
since I've been doing a great many things (none of which have been
knowingly tied to any sort of wake-on-lan, etc.). 

I've updated the BIOS and tried booting with pci=noacpi; no joy.

- Jeff