The program doesn't connect to my computer keyboard.

I have never connected the program to a MIDI.
That is, I always make my scores by inserting notes with a computer keyboard.
But now, it ignores my keyboard!!
For instance, it should turn into the insert-mode when pressing the "N" button, but it doesn't work.
(The problem being said can be dealt with mouse.)
Though, I can still use the mouse.
But later, when I try to insert the notes with the "A-B-C-D-E-F-G" buttons, it doesn't work again!!
I know that my problem can be temporarily fixed by just using the mouse, but it annoys me.
I will be grateful if you guys can me with it.
If there is any grammar mistake, I apologize for it since Eng isn't my mother tongue.
Sincerely,
Jerry, Lin