Providing terminal output
When posting terminal output, copy the output and paste it here, wrapped in three (3) backticks, before AND after the pasted text. Like this:
```
pasted text
```
This will just cause it to be rendered like this:
Sed
sollicitudin dolor
eget nisl elit id
condimentum
arcu erat varius
cursus sem quis eros.
Instead of like this:
Sed sollicitudin dolor eget nisl elit id condimentum arcu erat varius cursus sem quis eros.
Alternatively, paste the text you wish to format as terminal output, select all pasted text, and click the </> button on the taskbar. This will indent the whole pasted section with one TAB, causing it to render the same way as described above.
Thereby increasing legibility thus making it easier for those trying to provide assistance.
Now, taking an educated guess, I’d say this 
…is your keyboard, especially since you haven’t given any other information. So let’s see if a keypress is detected:
run the following in a terminal:
xinput test 7
And while that is running, press only the key that isn’t working.
If you accidentally press more keys, then start the process over.
Press Ctrl+C when done, to exit.
Provide any output here.