This afternoon I found myself without the ability to type into Spotlight on my new iMac running macOS 10.12.3. All other apps received keyboard input just fine. At the time I was using Spotlight to do some basic calculations involving adding two sums of money up. A bit of Googling lead me to this page, one answer for which was to restart the Spotlight process using the Terminal command “killall Spotlight”. That did the trick for me, Spotlight once again accepted keyboard input.