Ok, so I recently installed a pny geforce 6800 ultra in my computer (Athlon 2 ghz+, Asus A7n8x mobo, 512 mb ddr, 60 gb harddrive, antec 500 watt power supply). Now whenever I play HL2, or anything else, I get a BSOD with the message 'Kernel Stack fault' or some such thing after a short period of...