Originally Posted by kefkarz

Fans.. well, not many: just the CPU's (with heatsink), PSU's, and video card's. That could definitely be a problem,

To be quite honest, you need to put a case fan in the back pulling hot air out of the case. That is just a must! It is best also to have one in the front area pulling cool air in the case. This is just a guess, but that quite likely is the problem you are experiencing, because the heat is kind of trapped inside and things heat up real fast unless you have a smooth air flow from front to back. That is a pretty cheap affair to put those two in the case and definitely worth a try. With computers, heat kills, so keep that baby cool if you can. If you can fit a couple of 120mm fans in there, that would be even better than the 80mm fans, but do whatever you are able to do with your case.

but I think I'll try your suggestion with the extra fan blowing inside before I do (or buy) anything else. I'll be gone til tomorrow, so I won't respond to anything before then - but if anybody else can offer their input, it's appreciated.

We won't be able to rule out the power supply just yet as a possible cause as I mentioned earlier. If it were a choice between the PSU and the Motherboard, then I would say the PSU is it. However, with your lack of air flow, I am presently leaning toward heat as an issue you need to address ASAP. You should get an idea with the fan trick......let me know what the result of the fan trick is.