Black screens during gaming

Firtly i will give you some info about my pc:

proccesor: intel core 2 quad CPU @2.40Ghz
Ram: 4GB ddr2
Graphic card: Nvidia Ge Force 8800 GT
Graphic card's drivers: 8.17.12.5896
Windows 7 ultimate 64x
So my problem:

While i am playing a game (windowed mode mainly but happened of full mode as well) after some minutes (about..20) the monitor loses signal.Which means i have sound(not sure wether it just repeats the same part over and over again or the sound actually goes normal) but i get black screen and the monitor says "No signal'.
Weird part is that it doesn't happen to all games.So far it happened only on CoD:Black ops while football manager 2010 and pro evolution soccer 2010/2011 work without any problems.
If you need any more information let me know.
Thank you in advance

I'm having the same problem ... same situation. It doesn't happen on all games. Games that crash are Sacred 2 and Torchlight. Games that work... Civ 5 This has only occurred since the last Win 7 patch. processor: 3.05 gigahertz Intel Core i7 950 Ram 6GB Graphic card NVIDIA GeForce GTX 295 [Display adapter] (2x) Graphic Driver 8.17.11.9634 Win 7 Ultimate 64 Just wanted you to know you're not alone liakos1910

If there is a lot of us we could maybe make some club or something

Anyway...hope someone knows something about this cause it is really annoying man

i changed monitor and i don't have a problem so far (workin for like 30min now...while it never worked for 15min).
My other monitor was a "tv/monitor"...so if you have a same kind of monitor i suggest you to try and trade it or something to check wether this is the problem or not.
Hope it will indeed work for me and you will find a solution as well