Hello all. I just orderd and built a new system (4 days ago now), I installed Vista Ultimate x64 and my chipset, sound and gfx drivers (all latest certified) and then installed Vistas 2 service packs. Everything from desktop was fine. I then installed a game (Prototype) and loaded it with no problems. I configured video and control settings ok, and started a new game. About 5 minutes into the first mission the system locked up. No restart, no BSOD, no error message of any kind. I restarted the PC and got into windows again no problem. I tried Warhead, same problem, crashed within a couple of minutes of gameplay. I then tested an older game (COD: 2) and experienced the same problem. I checked my temps CPU: idle - 35 - 38*C / load (prime95) highest I saw was 45*C GPU: idle - 37 - 41*C / load (FurMark) highest temp reached before lock up was 73*C None of that seems at all high to me. Ran Vistas memtest next for ram, no errors found, double checked by installing last PC's memory, same problem. Tried a different hard disk with a fresh install of XP, same problem. Also tried various drivers at this point, including the ones that were supplied with the card, same problem. I thought it was one of two things, bad GPU or bad PSU. I put my old 8800GT in, crashes were gone...now I know this card doesn't have the power requirements of the GTX275, but still, if it was a faulty PSU surely it would still hang the system. Any thoughts or suggestions would be most welcome! System Specs: Intel E7400 Arctic Freezer 7 pro CPU cooling ASRock N7AD-SLI 4GB Geil RAM (2x2) DDR2 800Mhz WD250 Caviar OCZ StealthXStream 700watt Palit GTX275 Generic mid tower ATX case (1x92mm at rear, 1x120mm fan at front, 1x120mm at the side) Sorry for the massive post, just wanted it to be detailed. Thanks in advance.