alright well, as I said, you can test the monitor itself by using another device (such as a game console) that uses HDMI with the same cable.
That way we can narrow it down to one of three things:
HDMI cable.
Monitor panel.
HDMI port on the monitor.
(or perhaps a combination of the above)
But if using a different device yields results that say it's not the cable or the monitor, then we have to look at either the GPU/HDMI port on GPU or the drivers as the culprit.