Computers also gather dust. Good idea to open the cover and carefully clean it at least once a year(you can use a small vacuum, but I prefer taking mine outside and just blowing the crap out with compressed air).
BTW, same goes for Macs, too.
The temperature thing got me a few years ago. I needed a new system, had several parts, and pre-made systems were still fairly expensive. Built a 3' tower with three hard drives, three optical drives, and a bunch of other stuff. Damned thing started shutting down on me after 20-30 minutes, and I had built plenty of smaller systems before.
Got a free download of a temp monitor, and sure enough, all that hardware was just roasting inside. I had to run it with the sides off of the damned thing. Water-cooled systems were still very new back then, at least at the commercial level, and very spendy. Now you can get cases with built-in temp monitoring. If you don't have it, there is free software out there. I run such a program just to be sure I'm not toasting out one of my computers.