I've run the system with two of the three RAM modules removed, and rotated around the three modules to check each. It fails in the usual way sooner or later (one module ran OK from early afternoony yesterday through till nearly 2pm today) so I guess the RAM modues are not the problem part(s). Strange labelling on the RAM modules, each is labelled 6GB(3x2GB) 2048MB 1600MHz 8-8-8-24 1.65V ver3.2, they were bought together.
So, I am down to the graphics card, the mother board, the PSU, the i7 930 or the BIOS.
I think I have exhausted all of the things I can swap out without spending money, apart from the BIOS.
What next?
Rans6......