The center button does not work on EV3 brick
It is somewhat common for the buttons on the EV3 to stop working. This is usually caused by the failure of the adhesive that holds the metal part of the button in place. 

You can always contact LEGO customer support to see if they can help.

For the do-it-yourself person, it can be fixed fairly easily though. This is how I do it...

First, you will need to remove the cover from your EV3. This requires a Phillips screwdriver. Remove the 4 screws in the battery compartment and gently pull the top half of the plastic housing off.

The image below shows a couple buttons that I have already fixed and one button (the right button) where the adhesive has failed. You can see that the plastic covering is coming loose.



Use a sharp knife to cut away the plastic that has come loose. Since the adhesive is no longer sticky, it is not doing any good.





Use clear tape to fix the button back into place.




Then reassemble the EV3.