Modern monitors are all made in just a few factories, mostly in China. The chipsets can vary, but most of them meet the VESA standards set for industry, at least superficially.
Try replacing the cables. Whether a VGA cable, or an HDMI cable or a Displayport cable, there is a wide variance in cables that are hard to see. While working for monitor manufacturers, I always kept backup cables, just because. Not often needed, but invaluable when I found a problem during a demo or for a trade show. You would be surprised how often the most generic part was the problem that had to be replaced.
Today most people use a video chip on the motherboard, and only gamers and geeks end up buying the AMD or NVIDIA discrete video cards. But if the problem persists, try another video card, even the one that comes standard with your computer. Heat problems can mess up a video card or the system bus.
Look at this utility to see more about your setup: Moninfo
There are hundreds of videos, classes and seminars to learn this info in depth. The various video standards (VGA, HDMI, Displayport), video encoding standards, copy protection schemes and other issues can make this time consuming.
Start with a different cable, and then work outward from there.
Cable. Didn’t think of that. I am not the OP, however.
How about replacing the ram modules? Most modern computers that don’t have dedicated video cards use main ram for video. Bad ram bad image quality. Most desktop computers have all the ram n dual inline memory modules. If you have two you can take one out and move the other to a different slot. Take one out, test replace one with the other, test replace both with brand new, etc