Dell Laptop HDMI to Dell Monitor DisplayPort?

I am plugging a HDMI cable into the HDMI port on a Dell E5440 laptop and the other end of the cable, which is Display Port, into a Dell P1914S monitor.

Nothing shows on the external monitor no matter what I do or try on either the laptop or monitor?  I have tried this on a Dell E7000 series laptop also with no result on that one either?

Does the HDMI port on Dell laptops support video or do I need to utilise some other means of connecting a second monitor.  Bear in mind there is no VGA output on these laptops.

Thanks in advance

Wayne