I had a very similar problem recently except it would happen anywhere from 15-20 min into the game.Would happen with any game, DoD:S the most since I play it the most. Installed the latest drivers and all, but the problem still persisted on.
My Graphics card was over heating and would eventually temporarily give out. the card's Temperature would be normal until gaming, when it needed more juice, you could say. Regardless it couldn't breathe so it just kept giving out.
What did I do to fix it? I took the card out, dusted the crap out of it and cleaned it a tad (Be gentle if your doing this, a low powered vacuum or simply blowing on the card will do the trick. No slightly moist rags or paper towls or anything. That may seem a bit obvious, but your surprised what people do. In a nutshell, be gentle)
No problems ever since. My cards fan and the whole thing in general was just covered in dust, a lot of dust.