Hdmi Port not working.

Go to Device Manager and on the list of devices check for any devices ending with an exclamation point and delete them. Now click refresh at the top left or collapse n uncollapse the libraery or simply Reboot your system. Do not worry, this will not delete any device this will refresh the drivers back to their normal state. all Device Manager Drivers are stored in your operating system and reloads them on a refresh or if deleted.

When u reboot make sure the cable is connected so your system picks it up.

if you are plugging to a tv or monitor,

you must let your system know by going into the Display window in Settings and checking off the Add secondary Display in this section you can also mirror or deside wich display should be primery.

Lastly Should the above not work,

Check your Cmos, The HDMI feature could be turned off there. if it is, Activate it and hit F10 on your keyboard, pad or screen board. Good luck!