ASUS Motherboard sending one monitor to sleep

Hi Folks

Recently rebuilt the innards of my PC and the spec is currently :

Windows 7 Ultimate 64 bit
i3 3220
Asus P8z77-v LX Mobo
Asus Radeon HD 7700 2GB

Everything is basically peachy but I seem to have picked up an issue with one of the two monitors attached

At first I had assumed that the monitor had gone faulty, I have swapped all the cables with the other monitor but this made no difference. However, I noticed this morning that - from cold start, turning on PC then monitors, the ASUS logo appears on both screens and then the problem appears to occur, so for now I have ruled out the monitor. A few seconds after the ASUS logo pops up, one monitor carries on and is fine, the other, a Samsung Syncmaster 930BF goes the sleep and cannot be woken without pulling all the cables out the back and leaving it for a few minutes, at which point plugging it back in its then fine again. The Dell monitor is fine.

So I am assuming that either the Mobo BIOS or the graphics card is causing some sort of event with the monitor, but a bit stuck where to start. This is apparently before it starts windows so I would tend to be looking at the MOBO, but none of the settings I can find in the bios appear to relate to monitor settings - bios for the MOBO is July 2012 so it's hardly old.


Anyone have any ideas what could be causing this ?

Cheers

Alik.