So, I think I've finally, positively identified heat as the problem with the server. I installed a nifty little app called SpeedFan, which displays the fan speed and temperature gauges. After startup, the computer's temperature seemed steady at 48C, and crept slowly up to 50-52C, whereupon the icon changed to a fiery warning icon. It seems to be mostly stable somewhere in the low fifties, but every so often some process on the server spikes the CPU usage to 100%. This spike directly results in the CPU temperature jumping another four to eight degrees.
If the server manages to survive this spike, however brief, the machine remains running. If the failsafe mechanism kicks in, the server shuts off to preserve the CPU integrity. Basically, the computer runs uncommonly hot just as its usual state of being; when it's under heavy load, for reasons I cannot yet divine, it skirts dangerously close to (and then over) the failsafe limit.
So, as of right nowish, I'm heading out to go to Circuit City and pick up a new CPU fan. Something a little beefier should do the job. Right now I've got a frozen water bottle and a small fan (kinda like this) sitting next to the open case and trying to cool the thing. Yes, even with the new fan and a source of cold, the CPU is running at 53C on average. With luck, the new fan will do the trick and the server will remain standing... you know, outside of delicious Hot Pockets.
Update: Unfortunately my little trip to Circuit City, Best Buy and Radioshack was in vain. Each store had the same two or three Antec fans in stock and nothing else, and each store was more expensive than the last. So I went to Newegg and picked up not one, but three new fans for the price of one of the available brick-and-mortar items. This is the new processor heatsink I got; it should do a fine job. I think the one I have now just may be on its way out and requires replacing, and a case-installed fan should help additionally ventilate the heat away from the poor server. The machine, by the way, seems to be doing fine at a steady, slightly too-hot 52C, but as the processor tops out at 74C, this should be an okay stalemate until the parts arrive in three days.
Update the Second: For some reason the archive update script got stuck on something, caught itself in an endless loop, and jacked the CPU usage to 100%. This immediately resulted in the processor temperature jumping up to a dangerous 80C. I
am considering disabling have disabled the archive update script for the next couple days to ensure the stability of sup/tg/ in general. You can still add them, and attempting to re-add a thread will update it with the current contents, but I really don't want to accidentally fuck up the computer permanently because of a script mistake on my part.