Have you added or changed any hardware lately? If so try undoing those changes & see if that helps. I have had similiar problems to you when re-building an older PC once, it turned out that the graphics card was not properly making contact in the AGP slot.
I have just tried removing the vid card, reseating the CPU and since I have two strips of memory I tried each one individually and still no differance. Whats the chances of both memory strips going duff? Is it looking to be a choice between the mobo and power supply? I have also checked the bios battery, its 3.23V so thats looking ok.
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