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This is a quite common problem with electronic pianos and keyboards. Apparently power is On and the whole thing working fine, but no sound is produced by the keys.
Aside from, on some models and occasionally, the MIDI Mode having been enabled (which sends all playing out the MIDI Out port on the keyboard, but may mute the sound), this means an audio amplifier or audio amplifier stage in the keyboard has suffered an electronic defect, disabling it.
(Or in some types, a tone generator chip may have gone bad.)
You have not stated your keyboard or piano's maker nor model #. With those, I can tell you more about the problem and what to do about it, if you would Reply To Expert with that information, please.