Key "5" not responding while using a external keypad

Hi folksI just bought a notebook, and since i am used to fly with the keypadi bought an external keypad to use with notebook while flying FS9.But i dont know why the key nr "5" is not responding. Icannot assign the key to any function. For me it is importand thedefault use of key "5" to neutralize rudder etc while flying.Any hint how i can activate this key?RegardsAlex (LSZH)PMDG 747-400 pilot