I too am not able to dual display with my GeForce 8400 GS except in Linux.
Dual display monitor 1 loses signal after startup; Linux displays both
Windows 7 64 turns off the monitor 1 signal after startup. At login, it powers off monitor 1 and powers on monitor 2. Windows 7 behaves as though dual display is working even though monitor 1 does not display. It's the same for single display, the monitor will not work on cable 1 except at startup.
Both 'Extend these displays' in Windows Screen Resolution and 'Extend' in the Nvidia Control Panel is selected. And changing which one is primary does not turn on monitor 1. Nor does switching the position of display 1 in either (ex. left/right/top/bottom).
GeForce 8400 GS; Dual Monitor Solution 59 pin (
DMS-59) to 2 VGA adapter -tried two of these adapter cables.
Latest Driver: 306.23 - installed a clean reset install of the latest Nvidia driver released last week.
Same Resolution: 2 of the 4 monitors I have tried have the exact same 'recommended' resolution (1280X 1024), both 60Hz, and even chose 16 bit color for both instead of 32 to reduce resources.
Linux worked: Dual display worked immediately when I tried it in Ubuntu 10. So, it's not the hardware. It works in Ubuntu 12 too but not properly -it won't transfer windows across displays.
My Windows 7 64 is an upgrade from Vista 64. One person in another forum with the same problem resolved theirs by reinstalling Windows 7. But another got the same problem only after a fresh clean install of Windows 7 64 with the same GeForce 8400 GS and DMS-59 when it had previously worked in Vista.
Dual Monitors - Only One Works at a Time Pushing a menu button on monitor 1 does wake it up, but just says,
1: Analog Input in Power Save Mode
Press Any Key on Keyboard or Move Mouse