Due to Intellectual Property constraints, most notebook or laptop computers as well as desktop models do not have an HDMI port that allows video signals to be brought in via the HDMI port. It is an output only port. This prevents someone from being able to connect a DVD or BlueRay player to their computer and copy protected content. In general the only devices that can accept an HDMI signal and display it are televisions and monitors.

If you are trying to connect your D600 to an HDMI monitor or TV via the camera's USB port using a cable designed for an MHL compliant USB port (such as many mobile phones use to output video to a screen) it will not work since the USB port on your D600 is not MHL compliant. Use a mini-HDMI to HDMI cable to connect the mini-HDMI port on your camera to the HDMI port on a television or monitor.

If you want to shoot with your camera connected to a laptop to view your work as you shoot, you need to use a tethering capable application on your computer and connect the D600 to the computer via a mini-USB to USB cable. Even though many tethering applications allow you to control your camera from the computer, most also allow you to retain control using the camera itself.