Hello, I have just built a new computer and every once in a while when im playing games (COD4, WoW, Warcraft 3) My screen will lock up and then I will here a puttering noise from my headphones for about 4 seconds then nothing. I then have to hard boot my computer. Ive done a mem test for over 12 hours with no problems, CPU runs hotest at 55C, GPU about 70. Only thing i could think of was the GPU overheating but then I froze once when i was just installing a program. I also thought it might be my old IDE HD but then i took it out and installed windows on my SATA and it is still doing the same thing. I also do no overclocking what so ever. My specs are: AMD x2 +6400 XFX Geforce 8600GTS XXX Thermal Take V1 HSF MSI K9N SLI Platinum nForce 570 SLI Athlon 64/Athlon FX SktAM2 DDR2 ATX Motherboard w/Audio, Dual Gigabit LAN, RAID/Serial ATA Retail ASUS DRW-2014L1T 20X SATA DVD Burner Black Corsair TWIN2X2048-6400 2GB Kit DDR2-800 XMS2-6400 Xtreme Performance COOLER MASTER RP-650-PCAR eXtreme Power 650W Power Supply Retail
This sounds like a driver issue to me. Have you tried updating your video card drivers? This might help you find them: Drivers - NVIDIA Driver Downloads - Download Drivers
You can stress test your system with Orthos Stress Prime 2004. Just download it and see if your system experiences problems whilst its working. Be sure to give it a good run. On the face of it I would say either RAM, PSU or mobo burn-in seeing as its a new system.