|850Watt power supply tells us little. Please post the make and model number. There are cheap power supplies that are not really what they are rated when used in the real world. Giving us the details will allow us to see how likely you are running into power supply issues.|
As above, make sure that you have the latest driver for your graphics card, get the driver only from NVidia web site directly for your card and version of Windows.
Install HWMonitor and run it at idle for a while and then with the game launching, see if you can pick up anything really unusual like deep voltage drops, severe temperature rises, etc. one you launch the game. Report results.
You have to be a little bit crazy to keep you from going insane.