do you use the onboard graphic or a gpu card also check the monitor cable could be time to start looking for a upgrade .
Not sure how to answer your question. I've been using the standard monitor port for all these years. That's the one at the bottom of the image. I found this other one (top right in image) today. It had a grey plastic cap sealing it off.
As to the monitor wire, the monitor works just fine in another computer. When I tried, I tried it with the same wire. It is not the monitor nor is it the wire.