nouveau MGA3B2 does not detect 2nd monitor

This is my second installed MGA3 system and both display (no pun intended) the same problem on my multiscreen setup. Ttwo PCs with their own primary displays share a wide screen monitor via a Keyboard-Video-Mouse switch. The MGA2 system (call it A) is the one I have used to install MGA3. The B machine runs Mandriva 2010.1.
The A machine, when booted with MGA3, does not detect the second monitor (via the KVM) and does not initialise that output on the graphics card. When booted with MGA2 it works like it has always worked.
Does anyone know how to FORCE xorg/nouveau/kernel to activate a connected monitor it has forgotten how to detect?
Richard
The A machine, when booted with MGA3, does not detect the second monitor (via the KVM) and does not initialise that output on the graphics card. When booted with MGA2 it works like it has always worked.
Does anyone know how to FORCE xorg/nouveau/kernel to activate a connected monitor it has forgotten how to detect?
Richard