So, I was watching a movie on YouTube when I first noticed scanning lines distorting the picture on the bottom 1" of my Acer computer monitor. I figured it was embedded in the movie and thought no more about it until after the movie ended the scanning streaks didn't stop. Drat, I thought, now I'll need to buy a new monitor, but a second thought was that maybe I'd made a change that could be corrected, and I began troubleshooting, developing more theories, including the idea that maybe the problem was the display card and not the monitor. On the second day of wrestling with it I looked for helpful videos on YouTube and discovered that Acer scanning issues was a large topic, but many of them were produced by individuals who couldn't speak clear English and I got deeper into the weeds. Today was day three and I realized nothing I tried made any difference, and I hadn't learned anything. I'd even updated the display drivers. Maybe I could at least determine whether the trouble is in the computer or the monitor. But when I returned to the task I looked at the screen and it was a clear and pure as the day it was all new and fresh. The persistent scanning streaks were gone. The screen was normal as if it had fixed itself.
Maybe there are unseen spirits and an after-life.
Did you reseat the cables? I've had what I thought were glitchy monitors only to have the cable fall off the back at one point - reseating it and (gasp!), even attaching the screws fixed the problem.
In fact I did re-seat the VGA Monitor Cable but it didn't solve the scanning streaks, although I learned something else...
It so happens that the Acer Monitor has both VGA and HDMI inputs, so I wondered if switching might help, but I discovered that my HP8300 Mini-Tower does not have HDMI but does have "Display Port", for which I don't have the right cables.
I don't understand the scanning lines. Is the monitor an analog CRT like older computers used to be?
Answer: VGA is an analog video process, whereas HDMI & "Display Port" are digital.
The ACER Monitor is not CRT but is a flat screen computer monitor.
You might want to consider getting a Display Port to HDMI adapter (should be available on Amazon). If not, then you can definitely get a Display Port to DVI adapter, and then a DVI to HDMI adapter (I have both). You can probably get higher resolution and a better quality signal from the digital ports on your display card.
Days of struggle with screens and aspect ratios got resolved, much because of help from here at part15org, but as tends to happen, solving one problem opens the door to the next trouble.
All at once I found that I couldn't switch between my two computers using TightVNC, which has worked for years. My brain became foggy and I couldn't remember how it is supposed to work, so I took a blunt approach and uninstalled/reinstalled TightVNC. This went well at first, getting me back in touch with the other computer screen, but when I logged off I couldn't get back to the remote computer. I was back where I started.
For now I need to physically work from each computer until I get re-educated.