It could be that your CPU/Graphic card over heats. Dust does play a big role in most pc crashing.But then again the ram could have a bad block.
Try putting your pc in a clean room and clean it out a bit, then use a memory testing app such as
and do a overnight test or something to test ram. Then you might want to get a pc monitoring app such as
Motherbaord monitor http://downloads.guru3d.com/download.php?det=204
to see if your cpu is over heating. Also keep an eye on the north bridge temprature.