why doesn't the keys of macbook air won't turn on?

Try resetting your SMC.

Resetting the SMC of an Intel-based portable Mac with a battery you should not remove on your own

Note: This will not delete any data.

The SMC is responsible for controlling various system functions. None of your data will be deleted by resetting the SMC.

Shut down the computer by going to Apple () > Shut Down…

Select Shut Down or allow the computer to shut down automatically.

Plug in the MagSafe power adapter into a power source and then connect it to your Mac if you have not already done so.

On the built-in keyboard, press the (left side) Shift (⇧), Control (⌃), and Option (⌥) keys and the Power Button at the same time.

Release the (left side) Shift (⇧), Control (⌃), and Option (⌥) keys and the Power Button at the same time.

I hope I solved your question.

Austin