CANNOT TYPE e.g. Main Menu search, can't authenticate etc

[Nityanandi]

I necessarily tried in my new Debian 9 installation to change the keyboard layout to "English US international with dead keys", and don't recall changing any particular key settings, although i tried but changed mind about Hyper. (New to Debian, though i tried it very briefly over the many years with Linux, finding it too hard to set up new installations. And i LOVE Ian Murdock, our inestimable benefactor.)

Now i can't type even a single character in the Main Menu search and many other offline places, therefore cannot authenticate to open Synaptic Package Manager, cannot give myself sudo privileges, and find it hard to foresee how this can be fixed when the terminal won't let me control anything. What is more ... i didn't even GET the keyboard layout that i wanted, and i've gone back and changed it to En US and rebooted but the obstruction remains.

Input Method Configuration has this line: "Normal automatic choice: ibus (normally ibus or fcitx or uim)" but elsewhere i saw that fcitx is in use. Naturally ... i will be very very grateful if i don't have to reinstall and do all the hours of configuration again for something that can be fixed in a minute or two with help from the Linux family. We live by love.

[GarryRicketson]

To start with, have you checked the keyboard its self ? , and I don't mean, "think" it is ok , check that for sure, For example connect the keyboard to a different PC, that has a working keyboard, unplug the working keyboard, and plug in the one in question.
Or, boot with a "live medium", CD, USB, etc, does the keyboard work when you do that ?
If it is certain they keyboard does work, then take it from there.
Trying a different keyboard also , ... it may be by coincidence your keyboard, or the cable, (if it has one) failed at the same time you starting trying to make changes, Did it work before, ? and You say:

>>don't recall changing any particular key settings, although i tried but changed mind about Hyper.

If it was working before, then either you did change something, or maybe the keyboard itself just happened to fail at the same time.

All the "lovey dovey" junk is fine, but it does not give us any details that we can use to help you. For example what kind of keyboard, hardware, etc. ?

Realizing the catch 22, part if the system does not have the correct configuration, it can not detect and use the keyboard, and then you also can not type in any commands to change the configuration. If your mouse works,
you should be able to open a terminal, and copy / paste commands into the terminal, and even letters, (tedious but possible). On my system/mouse, I can send the "enter" signal by pressing the left button,and the scroll wheel at the same time.

There are 2 (maybe more)ways you can access the computer, maybe.
1st and easiest, boot with a "live" medium, CD, usb stick, assuming the problem is something you changed, and what you need to do is re-configure
the keyboard settings.
The "live CD", (medium) will detect your keyboard, and you can then access the system, from the Live disk.
https://manpages.debian.org/stretch/key ... .5.en.html
===================
https://wiki.debian.org/Keyboard
If your mouse works, you actually could just copy/paste the commands suggested in the above links, and re-configure the keyboard settings.
If your computer is part of a network, you could also maybe access from another computer, using ssh, and then fix the keyboard configuration.

[debiman]

I necessarily tried in my new Debian 9 installation to change the keyboard layout to "English US international with dead keys", and don't recall changing any particular key settings, although i tried but changed mind about Hyper.

Now i can't type even a single character in the Main Menu search and many other offline places, therefore cannot authenticate to open Synaptic Package Manager, cannot give myself sudo privileges, and find it hard to foresee how this can be fixed when the terminal won't let me control anything. What is more ... i didn't even GET the keyboard layout that i wanted, and i've gone back and changed it to En US and rebooted but the obstruction remains.

you have to show us how you "changed it back".
commands issued & output received.
use code tags for code.

also, have you checked debian wiki, then $SEARCHENGINE?