I've been running a 4 monitor setup with a GeForce 8800 GT (2xDVI) as the main graphics card, and a GeForce 8400 GS as the secondary (1xDVI, 1xVGA).
The 8800 GT got 2 DVI-monitors connected to it. The 8400 GS got 1 VGA-monitor + my HDTV connected via a DVI->HDMI adapter.
This setup has worked fine in Windows 7 for quite some time, until recently, when all of a sudden the 8400 GS does not allow me to use both the TV and the 3rd monitor at the same time. Instead when I try to do "Extend desktop to this display" under the Screen resolution dialog on the TV, I get an error "unable to save display settings".
Doing the same thing in the Nvidia control panel yields the error message "This GPU supports 1 display", only allowing me to enable either the VGA-monitor, or the TV, but not both at the same time.
Since I haven't used the computer since I've been away for a while, I'm not sure when this started happening exactly. I remember updating the driver for the 8400 via windows update a while back. I probably should mention I also had to do a CMOS reset recently, since the bios has gotten screwed somehow when the computer had been turned off for a long while.
I tried installing the latest driver from NVidias page, but that doesn't help at all. I also tried to downgrade to an older version, to no avail.
Does anyone have any idea what to do? I know the hardware supports this, so that's definantly not the issue.
I'm running Windows 7 64-bit.