Dell OptiPlex 960 (Late 2008) - Manual (Page 18)

18
Setting Up Your Computer
NOTE:
Connection of a DisplayPort monitor or adapter will result in the x16
PCI-Express slot being disabled. This is not a valid configuration. Remove the
PCI-Express card. Alternatively you may use the VGA port to connect a
display device if the PCI-Express card is not a graphics card.
3 Connect the monitor using a VGA cable.
4 Connect a USB device, such as a keyboard or mouse.