Nvidia second monitor will not display

[kteach]

Hello,
I just installed another Nvidia card today and both are having the same issue. They detect the secondary LCD monitor but will not display anything on it. Any experts out there?

 

[kteach]

To add more details. One computer is running Windows XP and the card was an 8400GS. The other computer is running Windows 7 and the card is 8600GT. Both are using the latest drivers from Nvidia. All screens, cables, and computers are in full working order. For one of them I swiched in an ATI 3450 and both screens work without a problem. Put the Nvidia back in and only one of the two displays will work (Yes I carefully removed and installed drivers).