Right it's not the power supply, took the power supply out of a working pc, and as soon as you connect the 4 pin the same thing happens. Is it worth stripping the graphics card and the ram off the motherboard and seeing if it makes any difference? Should I leave it on and see if it boots without the 4 pin connected? or is that inviting damage? Unfortunately i have no other compatible componenets that I can try to find out if one of other component is faulty. Is it worth taking the CPU off the mothboard and seeing if it still trips the power supply?