Hi have been working on a computer, here is the approximate spec: AMD athlon 2800+ 1GB ram DVD rom and CD writer 80gb HDD Creative sound card ( a fairly decent one) Nvidia Gforce FX 5950 Ultra New 500Watt power supply I have a problem in that when any sort of intence graphics take place, it switches off, and will not turn on until it is unplugged and re-plugged into the mains. For testing purposes I have been using 3d Benchmark, and When I run this it inveriably shuts down before the end of the tests (normally on CPU Test - is this Necessarily relevent?). I have tryed the Video card on another machine and that works fine. I have changed the power supply, no joy. I have just re-pasted the heatsink to the processor as I thought it was loosing contct (the old paste was very dry). The problem still persists, and whats more, nothing seems to be getting overly hot. I have felt the cpu heatsink and the graphics card after shut down and they seem ok, Also when I reboot and look at the temops, the CPU is at about 120 degrees whic doesnt seem exccessive does it (concidering my P4 runs at about 175 - and by the way, is that ok?)? If Anyone has any assumptions on whtat the most likely cause is, I would very much appreciate it.. Thanks in advance for any help.