problems with simple soundmanager

Question

I am trying to build my own soundmanager which is a singleton. I have 3 activities in my application:

MenuActivitie |+GameActivitie |+Settingsactivitie

In settings the user have the possibility to turn sound on an off. When I end the game and restart there is no sound is playing. This is my code... Where is my mistake?

package com.jb.sound;


import com.jb.R;
import android.content.Context;
import android.media.MediaPlayer;

public class SoundManager {

    static MediaPlayer mp;
    private static SoundManager instance = null;
    boolean play = false;
    static Context _context;

    private SoundManager(Context context){
        _context = context.getApplicationContext();

        mp = MediaPlayer.create(_context.getApplicationContext(),R.raw.uhr);
    }

    public static SoundManager getInstance(Context context){

        if(instance == null ){
            instance = new SoundManager(context);
        }    
        return instance;
    }

    public void soundStart(){
         mp.start();

    }

    public void soundStop(){
        mp.stop();
    }

    public boolean musicIsPlaying(){
        return play;
    }

}