Why does HDMI not work, but Mini Displayport does?

[stanleywinford]

I built a new PC, and used an old monitor (Dell Ultrasharp 19 inch) that has DVI-D and VGA connectors. On the other hand, my motherboard has HDMI and Mini Displayport connectors. When I connect the motherboard to the monitor's DVI-D port via a Mini Displayport to DVI-D adapter, everything works perfectly. When I connect it via a HDMI to DVI-D adapter, the monitor is completely blank.

Why is this the case? Does this indicate that the motherboard's HDMI port is broken?

My specs are:

Motherboard: Gigabyte Z170X Ultra Gaming
CPU: Core i5 7600
Hard disk: MyDigitalSSD BPX 80mm M.2 SSD
RAM: Corsair Vengeance LPX 16GB (2x8GB) DDR4
PSU: Corsair CX550M
Monitor: Dell UltraSharp 19 inch (might be an old monitor)
GPU: None

 

[cwli1_]

Likely. You need more equipment to be certain.