(This post is largely taken from discussion in #8045, #4448, and #9890)
Are you unable to type in the Windows Terminal, but every other application on your system seems to be running fine? Then you might need to manually enable the "Touch, Keyboard, and Handwriting Panel Service" in the OS. This (admittedly, poorly named) service is in charge of maintaining the modern input stack, which includes keyboard input.
You can confirm that the "Touch Keyboard and Handwriting Panel" service is running with the command:
sc query TabletInputService
Which should get you something like:
If you're seeing that the service is running, the next thing to check is if ctfmon.exe is also running. Apparently, ctfmon.exe is the real important process, which the service is just used to resurrect.
> tasklist /v /fi "imagename eq ctfmon.exe" /fo list
Image Name: ctfmon.exe
PID: 10828
Session Name: Console
Session#: 1
Mem Usage: 26,536 K
Status: Running
User Name: REDMOND\migrie
CPU Time: 0:01:05
Window Title: N/A
It needs to be running with a stable PID. So run that command a few times and make sure that the PID isn't changing.
Also, can you check InputServiceEnabled in the registry? You can do that with:
reg query hklm\software\microsoft\input /v InputServiceEnabled
Which should give you something like:
HKEY_LOCAL_MACHINE\software\microsoft\input
InputServiceEnabled REG_DWORD 0x1
If that fails, then it's possible some process is using msctfmonitor.dll in a way that's preventing ctfmon.exe from spawning successfully. To check this, run:
tasklist /m msctfmonitor.dll
That should produce output like:
PS C:\Users\ngupton> tasklist /m msctfmonitor.dll
Image Name PID Modules
========================= ======== ============================================
taskhostw.exe 12000 MsCtfMonitor.dll
If you see any processes in that output, go ahead and terminate them, then restart your PC. In this case, you'd taskkill /f /pid 12000 to kill process 12000. After rebooting, input should work once again.