When you have this issue you try this monitor on another PC and another monitor on this PC. Since you mention HDMI, a TV will do.
At this point you'll know if it's the PC or the monitor.
I’ve been having a problem with my computer. It is a gaming PC that I built my self. I have a gigabyte graphics card that is brand new along with the case and mother board. 2 days ago red horizontal lines popped up all over my screen and eventually at the end of the day they just disappeared on their own, after me trying many things to fix it and it failed.... Today again I turned my computer on this morning and the red lines were back! I’ve tried everything. It is not the monitor either (I tested with a different monitor) I have tried to switch from display port to HDMI and nothing works ... I’ve uninstalled and reinstalled the graphics card, updated the disc driver, and tried troubleshooting, and everything else I can thing of ... I am not sure what the problem is exactly ... but I just would like to get this fixed ASAP. Any help please!!

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