ah nevermind you dont support GTX NVIDIA graphics just read that.
You first who complains of a broken demo.
nV GTX cards is supported like any other cards with P.S. 3.0.
1) Check may be downloaded installation is broken?
2) Try start Encyclopedia by encycl.cmd or demo w/o intro by novideo.cmd in root game folder.
3) Try install demo to D:\Games not to Program Files
4) Try reinstall redists and DirectX from docs\support\redists folder