Hello, my name is Rusty. When individual keys go out, it's due to the velocity sensitive contact strips that are hit when you strike a key. They go bad, and they are a maintenance item. They are not too expensive. You'll need to take the piano apart to access the inside, so you can see the contact when you strike a key. You'll need to disconnect the old strip and replace it. Call(###) ###-####to order new strips. Once you put it back together, it will sound like new.
Click here. This will show you the insides of the piano. It's not your model, but yours is similar.