This just happened again. Two games in a row now all of a sudden. Ran a bootable ram tester and hotcpu tester last night. running off to go use 3dmark, but I'm really leaning towards it's a software problem since my hardware has been checking out AOK, and so many of the other games I play use so much more of the these resources. Game shut down from in game, to straight to desktop, no error or anything, all of a sudden just desktop.
on top of my specs above, games i have played on normal to full settings recently problem free: gears of war, command and conquer 3, earth 2150, assassin's creed, and frontlines fuel of war. these games are all much more graphics/cpu intensive and play fine with no crashes.
edit: i also run DG on the lowest settings possible due to fear of lag.