I know my system, and this is not a hardware issue. I built the system 3 years ago, and have never overclocked (this is a combo gaming/HTPC rig, so I keep things quiet and cool). I use way more PSU than I need, and my temps/airflow are good. Most importantly, I have 3 years of RPGs under my belt on this system, including many demanding 3D titles like Skyrim, Witcher 2, Dragon Age, and tons of others on the big screen at 1920x1080, and ONLY hit this problem when running PoE on my little desk monitor.
I only inquired about possible GPU types because I could see this being a driver issue of some kind. But if both AMD and Nvidia cards are hitting this, then nevermind.
This definitely is a very strange issue, and I do find it very odd that a simple Windows 7 application could bring down the whole system like this, going further than even a BSOD. You really don't see that much anymore in modern OSes.
And yet, after seeing this thread and that I'm not alone, I see no other alternative: Something in the PoE application code is causing an instant shutdown at random times for a VERY small sub-portion of the player base. Very strange....