[SOLVED] One monitor Isn't Working.

1: Debian Stable,
2: Just did a fresh install,
3: Second monitor does not work,
3a: the monitors are about 10 years old,
4: in desperation, I inserted a Knoppix Rescue Disk,
5: with Knoppix, I have two monitors again!
===
So... what's up with that?
I crawled under my desk and checked {unplugged and replugged} in EVERYTHING.
Apparently my second monitor isn't broken, but what's up with that?

PS: flatscreen LCD monitors "acer" models

Any suggestions?

Thank you for reading my posting, and have a great day!!

Again, not enough info Kevin. What GPU do you have? What is output from inxi -GSaz from an X terminal? Black display on vttys? Black display in X? Black display in both? Always, even at Grub/boot menu? Are you booting normally to GUI login screen? If so, which DM? SDDM? GDM? LightDM? Other? If at GUI login screen, does Ctrl-Alt-F3 produce a login prompt only on one display? Two? If two, does second remain if you switch back to X?

KDE version 5.20.5
KDE Frameworks Version: 5.78.0
QT Version 5.15.2
Kernel Version 10.10.0-21-AMD64
OS Type 64-bit

Processors 16 x AMD Ryzen 7 5800 8-core Processor
Memory 15.6 GiB of RAM
Graphics Prossor: iivimpipe

Always at GRUB boot

Everything, except for Knoppix, is blank

I guess I will download some rescue disk and see what happens!

Do you have firmware-amd-graphics installed in Debian?

xrandr -q

What happens when you post that at a command prompt?

I usually shuffle through the plethora of (often too many) GUI settings ta fix something like that but did you try a quick search like KDE won't detect my second monitor?

xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080
default connected 1920x1080+0+0 0mm x 0mm
1920x1080 77.00*

Also, I can have up to 4 monitors. I spent the time replace ALL monitors... to no effect

Originally Posted by kevinbenko xrandr: Failed to get size of gamma for output default

This is an expected result of running on a fallback driver, such as vesa or fbdev, an expected consequence of not having firmware-amd-graphics and/or libdrm-amdgpu1 and/or libgl1-mesa-dri installed.

Is it possible you have nVidia as here?
Maybe you need the proprietary driver.

Do you have non-free in your source list? I personally think depending on what you're doing, things aren't going to work well unless they're being worked on so have experimental in mine with ne'er a hitch. I mean LTS simply means old stuff! Sid (now RC-Buggy, testing and the like) doesn't brake toys muchmore, which also has changed its non-free's to non-free and non-free-firmware.

Add: https://www.debian.org/releases/book...non-free-split
i.e. https://www.debian.org/releases/

Went to the local computer guy {PC Parts & Supplies} about a week ago, I brought in my problem monitor, he checked it for less than a minute and told me that my monitor is dead {and most of that time was getting a connection} so, I bought myself another monitor, took it home, and it works, again!

Yeah the monitor is Ten years old.....

WINNING!!!!!

OK, I am calling this [SOLVED]