How to view the DB9 to USB port？？

I had a quick look at the manual for your board, you've have 2 ports on the M\B. one is soldered on and next to the VGA connector, the second is connected via an on board header, the connector is labeled COMB. You may have to open the computer and make sure that the cable is correctly connected.

If you have no luck with the on board ports a USB to Serial dongle or plugin serial card might be an option that has less hassles.

Not knowing the history of the machine if was used in an industrial setting the ports may have been damaged at some stage.

Hi !ALittleOffTheRails !
I opened the cover of the mainframe and found that my only DB9 was the "comb" connected to the motherboard, which was exactly the same as what you found in the information.
But now I can't use the only DB9. I'll listen to you and find a way.
"USB to serial dongle" is a kind of hardware, isn't it? I don't know much about this.
I normally consider whether to add "plugin serial card". Is this relatively simple?
As long as I can solve this problem, I am willing to pay some money to buy hardware
Thank you for your answer

Link to manual

download1.gigabyte.com/Files/Manual/mb_m...72ff025abbf17160ff2a

Page 4 of the manual shows COMA under the Printer connector and between the keyboard and VGA connector.

Something similar to this for USB to Serial\RS232, much much cheaper options available
au.element14.com/ftdi/ut232r-200/adaptor...-rs232-2m/dp/2352013

Serial port add in card (as an example)
www.startech.com/en-au/cards-adapters/pci1s550

Comparing the pinout on page 15 of the manual and the cable, usually the red wire deontes pin 1, the cable maybe connected the wrong way around.