The two hard disks seem to be getting toasty. I moved them apart a slot to see if that improves things. I don't have a fan or anything that I could stick there without compromising other parts.
Also double-checked the wiring, unplugged and replugged all power connectors. And felt around the SATA cables to make sure they're snug.
Went into BIOS settings one more time and discovered that memory voltage was set to 1.5v instead of the 1.65 indicated for the memory. Under-voltage fits the beeps, which were most closely ascribed to power errors, and memory errors would explain the crashing. And of course, absentmindedness.
http://www.bioscentral.com/beepcodes/awardbeep.htm Award bios beep codes
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