It should be one of those things you do every year, like changing batteries on your smoke detectors.
[note to self...install that smoke detector I bought 10 years ago....]
I'd been having shutdown issues on my 4-year-old PC, but only when I was running MCEBuddy, a program for converting MS Windows Media Center video to other formats. The program had always worked without trouble before, but in November of last year it started crashing the system.
I put it aside for a few months. Started messing with it late last night (well, early this morning). I set Windows 7 to show its "Blue Screen of Death" the next time there was a crash, got MCEBuddy going, and waited.
Fifteen minutes into converting this season's premier of "Justified," the computer simply shut off. No blue screen, no crash codes or anything. Didn't even have time to do a memory dump or write to a log. I tinkered for several hours, doing the usual stuff: upgrade the program, change to a different hard drive, look online for suggestions. Each time I'd get a few minutes into the video conversion and *CLICK* the PC turned off. Never a blue screen, always amnesia ("Why'd you turn me off? I didn't do anything wrong!").
I finally downloaded a little widget called Open Hardware Monitor. It gives you a table and a graph of an array of your system's stats like CPU, motherboard and video card temperatures, clock speeds, fan speeds and CPU loads. I ran the widget and set MCEBuddy to converting again.
The main motherboard and CPU temp graphs had been hovering in the 110F and 90F ranges, respectively, but as the program kicked in both temps started going up and up and up. I don't know how accurate the reporting is (there's a temperature-reading error on earlier AMD Athlon II X2 processors), but the widget pegged my CPU's temp at 212F (the motherboard's was closer to 220F!) before the system shut down as before.
And that was with both sides of the case removed to let more air in. So much for it just being bad fans.
I pulled the heat sink off the CPU and found a layer of dust buildup between it and the fan. It might not have been 212F, but the sink was too hot to handle. A little brushwork and it was clean. Didn't put new conductive grease on (got to wait for payday), but I did a little dusting around the board before firing the thing up again.
Now the temps are running 131F/122F at most for the mobo and CPU, respectively, for 12 hours even with MCEBuddy running and pulling 90% to 100% of CPU load.
Time to pull the system apart and hit the graphics card's fans and sinks. It's running around 135F on the low end and 152F max. It's got to be in the current card slot, but maybe I can move some of the others around to get more air in there.