Might this help?
Sometimes, accidentally brushing over the keys triggers the Numlock button...or the cat walking on it...
Keyboards which do not have a number keypad, use the Numlock button to convert almost the whole right side of the board, into a number pad, and some symbols.
While in that mode, one can use the Fn button, to toggle between using letters or numbers.
To stop using the right side of the board as a number keypad, press the Numlock button to shut it off, getting the letters back.