Your notations reflect an issue with the video drivers. If this is not a new setup, then you might try looking into a nVidia driver cleaning utility and reinstall an older version that you know is stable. If it is a new setup, then try uninstalling the video card and removing the drivers and reinstalling.
It could also very well be a power problem. You are running a high-end video card and a 500w PSU. Though PCP&C makes a decent product, how much power do you have on the 12v rail? Since your problems crop up when playing 3D games, it is very possible that your video card is simply starving for power... and when it doesn't get enough it hacks up a hairball and BSOD's on you.