Anne Wilson wrote: . . .
I do have a UPS, and it's fully charged. The system is just spontaneously rebooting or shutting down.
http://en.wikipedia.org/wiki/Capacitor_plague.
I just fixed a test box that kept getting something like "received INT 11 - no one cared" and then locks up. Replaced two caps - I yanked them from some old, defunct power supplies.