Sounds like something's overheating. I had a similar problem with Fallout 3. I could play the game for as long as I wanted, or just for 5 minutes, but my PC would always shut itself down during a specific conversation with an NPC. Turns out the game was throwing a lot of extra crap out during that particular conversation for some reason and my GPU was overheating.
If you can find a monitoring tool, run it while you're playing the game and keep an eye on the temperatures of your GPU and CPU (and others, just in case). Just put it up on a second monitor if you have one, or check the log after you've restarted, assuming it keeps them.
Thanks, it is probably that.
This game is incredibly GPU intensive. Ludicrously and unneccesarily so... The Witcher 2 with Ubersampling is less intensive than this one in comparison.
Free monitoring tool: Link
Shows temperature, and allows you to change the speed of all your fans.
No not those fans, the ones in the PC.
[Edited by Monkey007, 4/28/2012 6:44:28 PM]
Near as I can tell, most people experiencing issues or high usage is due to not having the latest NVIDIA beta drivers. (for NVIDIA users, anyway) Otherwise the game causes massive memory leaks such.
And just to help narrow down the cause of the issue (or pretty much any issue for any game, really) it is a good idea to use a program (or two, if they separate) that monitors GPU temperature and CPU temperature. Depending on how old your hardware is, "safe" operating temps can range from 75°C (on really, really old hardware) to 90-95°C. (on the newest stuff) If you're not hitting those temperatures then you shouldn't get any hard locks.