Damn, RMA time for me. My motherboard has developed a fault were the system after its been shutdown switches itself back on after 2 seconds. At first I thought it must be a windows issue but now all I have connected is the cpu, 1 stick of ram and the psu (no mouse, keyboard or any systems cables) - and it still restarts itself.

I've tried all the bioses available and pulled the battery for a while to get a full reset. I even tried a different psu to rule that out.

Oh well..