Pry off the "A" key and clean out anything around the stump. Replace it and try it. If that doesn't work, try using a pencil to activate the mechanisim inside. Still not working, call Applecare (800)APL-CARE and they will help you get it fix if its new, or under Applecare. Otherwise go to a computer store and buy a new USB keyboard.
If you switch the keyboard layout to French, the letter "q" will become an "a".
Ya know, the US layout aka QWERTY, the French (and Belgian) aka AZERTY... thus the first two letters being A, Z, ....