Hold power button down before opening up camera to see if something is broken, first... Check if Shutter Button is in good condition, then remove battery to force a shut down. If the power button is loose, stuck, or otherwise unresponsive, replacement may be necessary.
If camera is not responding, soak your phone in 99% Isopropyl Alcohol for about two hours. Having that done, put camera in a bag of uncooked rice for a few hours.