GIGABYTE Z270X-UD3 and Intel i5 7600K: HDMI VGA light is red no display

[heyong]

It's a new build, my specs are:

Motherboard: GIGABYTE Z270X-UD3
CPU: Intel i5 7600K
RAM: Kingston Fury DDR4 2400 8G *2
SSD: SAMSUNG 850 EVO 250G SATA3
Power: Antec 500W VP500P
Monitor: AOC LV243WUP 23.6 4K

When the HDMI is plugged in on the motherboard, I am getting the VGA light red. But if I power off and unplug the HDMI from the motherboard, all 4 lights are off.

The monitor is fine, cause I am using it as a external monitor for my macbook pro. This is also my first build and noob friendly terms are appreciated.

 

[Kasper Jorgensen]

Are you using onboard graphics or do you have a GPU installed and which?

 

[heyong]

Are you using onboard graphics or do you have a GPU installed and which?

I am using the onboard graphics. Do I need to purchase another video card to make it work?