It's not about overheating, the same thing happens to me. My wife and I both run the game on standard, no shadows, no AA, no physics, no footstep effects, and yet I constantly get an "unable to detect DirectX device" and she does not. Her computer is significantly worse than mine.
It is worth noting that SE has already had numerous crash problems with the 260.99 drivers (belonging to the Nvidia 200, 300, 400, and others), although rolling back the drivers (at least in my case) does nothing to improve the scenario.
There are numerous other forums that talk about this problem, none of which has helped. Most of them mention the same few fixes: turn down graphics, update/rollback drivers, tinker with other settings, but it is unlikely that any will actually work.
Like me, it seems that you will simply have to wait for a fix... assuming SE even realises that the "unable to detect DirectX device" issue is a relatively wide-spread one.
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