Where I live, the outside temperature rarely goes above 70F (even in the summer). However, when it does, the temperature in my computer room is probably 80ish and for some reason my rig freezes frequently under load while gaming, but only in these circumstances, which leads me to believe that this issue is almost certainly heat related.
I haven't overclocked my phenom x4 955, and I have a Xigmatek aftermarket cooler on it. I ran speedfan on my secondary monitor while I was gaming today, and took a picture with my crappy phone camera of what the last settings were before it crashed under load.
This is what it looks like in the same conditions idling.