win7 only 3 out of 4 monitors work

I have a dell machine here with 2 hd3400 cards.

I can only get 3 out of the 4 monitors to work.

it is not the cables nor the monitors, it's not the card either because if i unplug one of the working ones, the one that wasn't working comes on.

the 4th monitor has the light on as if it has a signal but the screen is black.

this is a windows 7 32 bit machine.

Any ideas?

A quick google search comes up with:

download the latest driver
from nVidia, disconnect from the network, uninstall the driver, reboot and do not let Windows try to install the driver. Then, install the driver you previously downloaded.

Once I did that and rebooted, I was again back to three displays. But once I went into the nVidia control panel, it let me enable the 4th display.

Click to expand...

try that maybe and post back with your results