While playing "FlatOut" demo, the PC crashes & a blue screen error appears with a STOP message saying that an error occured in "nv4_disp.dll"....any help plzz?

Usually you need to install drivers whilst in admin mode.
type dxdiag in run menu, go to diplay, and look at last four digits of driver version.

Another way of doing this is to go to your Device Manager. Click on Display Adapters. Right click your video card and select properites. Click on the Drivers Tab and it should be displayed in there.

Driver Version: 6693....now what should i do?

see if this helps

Games: "Stop" Error Message That References Nv4_disp.dll