8800GT and blank screen while trying Grid demo

here is the problem.

when i want to play the demo of Grid. the game sometimes wont start, thats not a problem. it crashes, thats not a problem. but sometimes, while playing the race, the screen will be *out of signal*. n i have to restart my pc.

the temp are not that great. 65+c.

knowing that i've being playing other games as well, crysis, cod4 with NO problems. hell ive have spend the last day playing cod4 online without a single crash!

Well i have heard of signal out of range when you set the refresh out side of what the monitor can handle.
Could just be a poorly coded demo with glitches and bugs in it.
Do you loose sound and picture at the same time, if so this sugests that the game is hanging/frezing etc but if you keep the sound its more likley to be a software issue with the video.
You could try turning down your refresh rate and turning a few effects of in the graphics drivers.
I dont think you have a hardware issue as i can see from your sig that your not lacking in that department, it may just be a conflict with a bad demo download and your set up.
I have had demo's not work properly before and then been ok after be ing reinstalled.
Not exactly an answer but a few ideas
hope it helps
Mactronix