Key 'A' is not working

When I press key A in input mode, it doesn't insert note A as it should do.
But when I press shift+A, it will insert note A into the chord normally, so it doesn't seem to be a problem with my keyboard.
I have also noticed that when I switch to French input method (where key A and key Q are swapped) and I press key Q, it will insert note A normally. But it doesn't work with English input method. Weird.