Strange, I have this problem if I use the inline client (win7 64bit, NVIDIA, too).
Which DX9 client version do you use?
Anything "interesting" or red in Orbiter\Modules\D3D9Client\D3D9ClientLog.html?
Do you use the most recent NVIDIA drivers?
...and it looks like the DX11 won't work with it, it's a DX10 graphics adapter: http://en.wikipedia.org/wiki/GeForce_200_Series