Have you tried lowering the graphics settings and resolution, or switching to Windowed or Fake Fullscreen display mode, to see if that would make a difference? One person reported stability problems in D:OS if they had Ambient Occlusion enabled, for example, but the game was fine if they disabled it and enabled it in their graphics drivers. You could try disabling all the post processing in the graphics options, etc. Another was getting random reboots, which they tracked down to the graphics options in any game being different than was set as default in their video drivers (for anti-aliasing, ambient occlusion, etc).
Do you have Vsync enabled, or the frame rate cap set in the options? Try enabling, lowering or disabling those options.
Try resetting your graphics driver's 3D settings to default (right click an open area of the desktop to start the nvidia Control Panel).
It couldn't hurt to try verifying local files: in the Steam library, right click on the game and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.
Check for updated graphics drivers and Windows updates in general.
