I appreciate the help but I can't begin to explain how much testing I have done on this problem...
I've tried pretty much every bios setting available with no positive result, Windows with no drivers installed, with the supplied DVD drivers installed, and then with the latest drivers from the website installed, no change.
Different graphics cards (geforce, quadro, ati) all no change.
Different RAM, no change.
When I switch everything on to an ASUS X79 board everything works perfectly.
Please be clear, the machine will sleep if I manually ask it too, it will not sleep the monitors (or auto start a screensaver) on a timed schedule of inactivity. We build quite a lot of computers here and apart from this issue we like using the X79-UD3 board but this is making it impossible for us to use it moving forwards. As I said before, it is not just one system that has the problem, every build we do using this board is affected.
Have you any further ideas, or can anyone else verify that their board doesn't have the issue.
Thanks gain for the reply.