Ok guys i need help, 4 days ago my computer randomly started locking up, the screen just freezes, i cant cntrl, alt, delete, the cursor is just stuck and there is no acctivity from the hard drive, the only way to get out is to reset the computer, it has done it a few times whilst browsing the internet, but i cannot play any games as it locks up straight away. Here are the things i have tried, Run anti virus and spyware scans Reinstalled windows Run memtest, no errors reported Run the seagate hard drive diagnostic program, no errors reported Updated chipset and bios Cleaned cpu heatsink and all fans None of the above have worked, but i think i have tracked it down to either a faulty graphics card or a faulty psu. If i swop the graphics card to the original nvidia 6800gt that came with the system it doesnt lock up. So here lies my quandry, is it the card or the psu ? A year ago i purchased a new Gainward Bliss 7800gs and it has been running perfectly up until now, but the power requirement is for a 400watt psu, my psu is 480 watts. The 6800gt power requirement is for a 350 watt psu, it's not much difference i know but it could be that my psu is failing and doesnt have enough juice to power the 7800gs. Heres the weird thing if i look in my bios there is no 12v rail reading anywhere, so i tried everest and again there is no 12v rail reading, also speedfan shows no 12v rail reading, could this be my problem ? I need to know if it is indeed the psu before purchasing a new one, i have another computer that i could try the 7800gs in but the psu is only 350 watt so i dont think it would work anyway. I purchased this rig 3 years ago and it has been running fine untill now, here are the specs ALIENWARE AURORA-FX ABIT AV8 SOCKET 939 MOTHERBOARD AMD ATHLON FX55 CPU 2GB DDR PC3200 RAM 120GB SEAGATE BARRACUDA HARD DRIVE AUDIGY 2 ZS SOUND CARD LITE ON CD-RW DRIVE 16X DVD-ROM 480 WATT ALIENWARE PSU GAINWARD BLISS 700GS OR NVIDIA 6800GT So any ideas what is at fault the psu or gpu, and why is there no 12v rail reading anywhere ? Many thanks.