When you start PowerShell and you are not able to enter any commands (copy/paste might still work), chances are your PSReadLine module is outdated.

Fix: Update PSReadLine module
Get-Module PSReadLine
Version 2.0.0

# Open cmd.exe as admin and run:
powershell -noprofile -command "Install-Module PSReadLine -Force"

Get-Module PSReadLine
Version 2.2.6