If the keys respond when transposing octaves, this should be restored via a firmware reset:
_ switch off the keyboard;
_ press and hold both (+) and (-) buttons while switching on the keyboard;
_ LEDs are blinking and going from 1 to 8, then light off;
_ restart the keyboard and test if everything runs fine.
If the keys do not respond even when transposing octaves, the problem seems to be mechanical, then a gentle visit to your favorite dealer for an exchange shall solve it all.