Update, I definitely think there is a problem with the motherboard. I boot up the board and it will go to bios with either the new or old cpu. I then try to reboot it - nothing.
Connect seperate things, nothing.
Take it back to basics, reseat cpu and it works once again (only once though).
So ruddy annoying. Going to ring up scan now to see if they can do a quick swap of the motherboard.
Cheers, Ian