wk-3300 The first 7 key of my CASIO WK-3300 doesn't make any sound but the piano detects them.

[JoseLuis12]

Hi, my brother gave me his WK-3300 but i don't know why the the seven first keys doesn't work at all, the screens shows that the key is pressed but it doesn't make any sound. Also the key "keeps pressed" on the screen, I tried to factory reset it but it still happens. These keys in the photo are the ones that stay on when I press them. Hope it has a solution, thanks! 

[eldo gultom]

have you tried reset them? in my wK 1800, reset is (+) + (-) and (enter) keys pressed together