But that's an entirely different thing. It's not "black lines", and it's not just the graphics card. If the mouse cursor won't go into that area, it's simply the edge of the screen.
The black lines I witnessed weren't as severe as some of the black lines I've read about. They don't go through the entire screen or anything. Right now, at the current resolution, there's a black rectangle at the top of the screen, and I can't move my mouse cursor past it. The tip of the cursor will stop right at the black line. So I'm pretty much losing 10-20 pixels off the top of my screen, which isn't much of an inconvenience, but I'm still curious about what the problem is. As I said, the size of the lines depends on the resolution. If I recall correctly, they'll only spawn on the top/bottom of the monitor, not anywhere else.
This sounds to me like you're either using a resolution lower than the native one on a LCD that doesn't scale (this can be turned on/off in the on-screen menu on some) or an old CRT (does anyone still use these?). I remember having this kind of thing once some years ago accidentially using 1280x960 on a LCD that had a physical resolution of 1280x1024, and I remember CRTs sometimes did weird stuff to scalng the image with different resolutions and refresh rates (though I have no idea why). Having to to turn the little knobs on the bottom used to be not at all a rare thing in the 90s.
So, be sure the actual resolution in your settings is the native one before worrying about anything else.