It appears you have an Inspiron 660s. This computer has one PCI-e X16 and one PCI-e x1 slot. The computer was designed to accept a PCI-e X16 video card, such as the card visible in your graphic at the top of the rear panel. The slot beneath is the PCI-e X1 slot.
If you are replacing the existing video card in the X16 slot (or your computer presently has no video card in that slot), you need the X16 card that matches the connector. If you are attempting to add a second video card, you must use a card that will fit the PCI-e X1 slot.