After recent windows update many users are experiencing keys not working in sticky note, for some users only backspace and delete key works. Here is the temporary fix till microsoft roll out fix in future update.
Right click Taskbar and open Task Manager.
In Processes tab find sticky notes(you can also hit “S” key couple of time to find it faster). Right click sticky note from list and choose End Task.
open start menu and type “sticky note” then click sticky note from result to open it.
now keys will work in sticky notes. This works for most users. if it didnt, wait for next sticky note or windows update.