Screen and graphics are just jumping, flickering and doing random things

[sillysack69]

My Samsung Galaxy S5 Sprint (carrier unlocked) with Android 6.0.1 has suddenly been acting weird. The screen and graphics are flickering and jumping about the LCD screen. Once it even turned the screen negative with black and orange colors. I manually went to accessibility settings and enabled negative colors so that the screen went to normal.…That is until it again went negative and I had to turn off negative colors afterward. I don't know what is causing this and I want to badly fix it.
Specifications:
Android Version: 6.0.1 from Lollipop
Rooted: Yes (probably since it had SuperSU already installed when I got it)

Now I haven't Factory Reset it yet because I fear that resetting it to factory default while it is rooted might break it. I don't know how to unroot it either. I will be helpful knowing if I can safely reset it with it still rooted.

Edit: I also want to say that whenever I try to share my PC internet connection to the phone, the phone somehow manages to crash my PC every time. I can find no fix for any of these problems. I am so helpless and hopeless…

 

[underway99]

This could be hardware or software. It's easier to troubleshoot the software side. I'd first reverse any recent changes. What did you do to the phone right before it started showing the issue?

If the phone has a superuser utility, then it likely is or was rooted. A factory data reset (FDR) will normally break root, but not all the way. It won't reflash the stock recovery. You'll have to do that yourself if you don't care to keep the root. Otherwise, you'll have to root it again.

If you don't care to keep the phone rooted, consider just reloading the stock firmware. That will completely wipe any traces of the rooted software and make the phone like it came from the box, including the stock recovery. You have to be very careful because it is also very easy to brick your phone if the process does not complete correctly. Understand how the process works, why it works as it does, and how to recover if things go wrong. The best place to go for detailed help on reflashing and such is at XDA. The folks over there live and breathe this stuff. Many of those folks are here too, but the discussion gets deeper there.

You will lose everything on your phone. So make sure that all of your photos, docs, music, etc are backed up. I also unmount and remove my SD card before I reflash anything. Every once in a while, people report that they've had their SD card go bad when reflashing or doing an update. It doesn't hurt to be safe.

The actual process for reflashing the older OS is just a matter of downloading ODIN (that's Samsung's maintenance utility) and finding the right firmware package for your device. You can't mix and match here. Your phone won't work with the incorrect OS.

To give you an idea of what is involved, look at this tutorial from one of the mods here.

[Guide][Samsung] How to flash Stock ROM via ODIN with the New Interface