Earlier today, I found that one of my boxen had hung. I tried restarting it, but was met with a keening siren alarm from my motherboard. Giving it a rest and restarting was either producing the same siren or a hang after a few minutes along with some nifty monitor graffiti.
My manual told me that the siren was my BIOS triggering a temperature alarm. So, after a couple of restarts, I got into my BIOS and sniffed around for the right place to find temperature sensor information and finally found it under "Hardware monitors". Sure enough, my motherboard temperature was at 95C! Too warm for school, I'd say. My CPU temperature, which was what I'd thought would have been the cause of the high temperature warning, was at a more sedate 49C.
So, now that I knew what the problem apparently was, I had to find a solution. Googling told me that the usual suspects for motherboard temperature warnings were leaky capacitors and generally.. old parts and otherwise the accumulation of dust and lint and possibly the blocking of air flows.
It was recommended that I pore over the motherboard looking for capacitors with corroded, crusty-deposit look about them. None found.
Next up, dust (and there was a lot of it). So, off I went ... First up, I disconnected all cables and set them aside. I then removed the memory modules; removed the PCI cards; removed the CPU heatsink for good measure and then spent a good two hours wiping the motherboard clean including around the capacitors, the memory and expansion slots, and made sure to get those "hard-to-reach" places too. Next, I cleaned all the fans - the heatsink fan, the case fan and the vanes of the heatsink itself. I also managed to clean the SMPS unit so that it didn't feel left out.
Now that my conscience was clear, I reconnected everything, made sure that nothing was obstructing the fans (which incidentally, all blow in) and booted the PC and voila! got a temperature of 37C which since then, has peaked off at 44C. The PC is also quieter than before.
Time well spent. Hope this helps others out there :)