Ok, so yesterday I installed a brand new Sapphire 4770, which I was having a fair bit of trouble with (see this thread for details). In brief, the card just wasn't performing as well as it should have been. It was suggested it may have been the PSU, but I recokened a 450W with two 18amp 12V rails should have been enough (and I was hardly overloading the system). So, I thought it might have been a driver issue. My previous card was a 7900GT, so I went through safe mode to remove all the old drivers with Driver Sweeper. It left nTune in, so I was manually removing the remnents of the application in the Registry Editor when POOF... off goes the PC. There's still some life left in it, with it all plugged in the Capslock light still works and the Motherboard LED lights up, but upon pressing the power button it boots up for prehaps a milisecond, and then switches itself off again. The Capslock light etc. still work, but it won't turn on again. Switching it off and on at the back switch resets this, but doesn't improve anything. I tried disconnecting the new GPU and every possible periphery, no difference. I presume it's the PSU and I need a replacement, but before I splash £50 out on a new one, has anyone got any ideas as to what else it might be? My full system spec is: CPU: Pentium 4 CPU 3.4 Ghz | RAM: 1Gb + 2x512Mb Corsair DDR2 667 Mhz | HDD: WD Raptor 36Gb, Seagate 300Gb | MB: Asus P5LD2 SE | PSU: FG ATX-450PAF (450W, dual 12V rails at 18amps each) + an old 7900GT or a new Sapphire 4770 depending. Any help would be really appreciated!