Need a lot more info. You said a long time...how long? Assuming it’s a desktop, what brand and model is the video card. What resolution is the monitor and what resolution is the card configured for (settings in Windows)? How old is the computer?
As to the cable, I think that the cable is part of the monitor (though I could be wrong; I'll check). As for the card, I don't have the slightest idea how to open a computer, much less look for or replace a card.
The computer is pretty old. I bought it used seven years ago, and I think the date when it comes on says 2016 (to check I'd have to reboot and lose this text). The thing is, it was actually a business computer and was supposedly worth much, much more than I paid for it. And it has lasted the longest and offered the least trouble of any computer I've ever owned. Of course, support for Windows 10 is ending soon, and I'll have to deal with that (way too much on my plate right now and money is the tightest it's ever been). But I can always consult with my bro-in-law or the people at the place that sold it too me. Unfortunately I'm not a member of Geek Squad. If (or when) I get another computer I'll want all my stuff put on it, and I don't know how to do that either.
At any rate, the problem right now (merely cosmetic though it is) is more distracting than it's ever been (before Windows even loads the computer logo bleeds rightward across the screen). And there is still the fact that this never happened with the unsatisfactory smaller screens.
Thank you all, and if anyone else has any other suggestion, please add it!