Actually im getting a similar thing, and ive tried a number of different things to try cure it. But, i think its my vid card. I overclocked it, and theres an option to say restore these settings on reboot, which i checked (this is so if it becomes unstable it will revert back to a known good setting on next reboot if you dont check that box). Now when i suspected it may have been the vid card and my OC'ing of it, i went into the card properties and turned overclocking off, but totally forgot to clear the checkbox. So next time i rebooted it reverted back to the overclocked position, and it still continued to lock up randomly. So i dismissed the overclocked card as the issue. What i have only just realised is that its still running in the overclocked mode.
I guess, its a matter of trying one thing at a time till it dissapears. Which may take a while. BUt make sure you are certain about the assumptions you are making...
PS - i havent got round to trying it since i realised my card was still OC'd only last night... Will let ya know if that was it after a few weeks of flying...