Camera and Video
Ask a Camera and Video Question, Get an Answer ASAP!
The electrical contacts beneath the button can wear out over time, or moisture and grease can seep in and coat the contacts, preventing them from working all the time.
The camera will need to be disassembled and the electrical contacts can first be inspected and cleaned to see if that works.
If the contacts are worn out or damaged then the button assembly will need to be replaced.
A local electronics or camera repair shop can do this for you - it is a fairly common repair; or you can return the camera to Nikon for repair: http://www.nikonusa.com/en/service-and-support/service-and-repair.page