Anyway, as I said in the OP, it may not have anything to do with the game. But maybe in the alpha the game engine is not as efficient as it will be later. *shrugs*
During any alpha or beta test, you can expect debugging features to be turned on, and that they will be turned off for the full release. But I don't think this is your problem. And with your load showing 75% (high, yes, but not unreasonable) I have difficulty seeing this as a cause.
Your graphics card certainly meets minimum requirements as stated in the Steam description of the game.
Something has to trigger the shutdown, and I don't think the game could do that by itself. My first thought was temperature, but the temps you gave us are certainly not enough to cause it. I would not expect temperature to cause a shutdown until the graphics card had declocked several times, in which case I would expect you to see continuingly degrading performance.
So now we get to the more remote possible causes, and I suspect you are already guessing what I am thinking of and probably have already checked for them, but here it is anyway. -- Have you checked for viruses, adware, and browser hijackers?
One other thought: you mentioned you have an Intel I7, but you didn't mention what model.
From here on I find myself grasping for straws as to what the problem might be (perhaps I am already) and if this doesn't help you may have to find a better qualified person to track the problem down.
