Problem with 9600gt oc sleep mode

Hello, hmm. i just bought a video card Nvidia 9600 Gt OC and i have problem.
When i turn on the computer, i have screen like regular , yea, so my fan cooler working well, then when comes a Windows XP logo and loading bar, after flashing light in Keyboard (like loaded) so my fan is works very slow,
K when i am starting games(2006-2008) and playing like 20 min, if make like too much exploads, so i have on screen message : Monitor going sleep… And my PC like stuck,
so i turn off power and power on,
Or i staring Generals Zero Hour game. after 3 min playing game its come like that,
SO guys I have Intel® Core™2CPU 6400@ 2.13ghz, 1.60ghz,200gb ram, Windows Xp Media center PC
Please help

You will have more luck in a forum about graphics, this is about CUDA.