Play sound when a button is pressed on Android

I'm new to Android, and I'm trying to do something simple, like playing custom MP3s when a button is pressed. It looks like a question , but although my code follows the examples and I get no errors, I can not hear any sound either in the simulator or in the real phone.

My MainActivity.java:

public class MainActivity extends Activity {

    private static final String TAG = "MyActivity";

    public void MyActivity(Bundle onSavedStateInstance) {
        Log.v(TAG, "Initializing sounds...");

        final MediaPlayer mp = MediaPlayer.create(this, R.raw.alarma_67560);

        Button play_button = (Button)this.findViewById(R.id.play_button);
        play_button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Log.v(TAG, "Playing sound...");
                mp.start();
            }
        });
        Log.v(TAG, "Sounds initialized.");
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

And my activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:padding="@dimen/padding_medium"
        android:text="@string/hello_world"
        tools:context=".MainActivity" />

    <Button
        android:id="@+id/play_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/play_button" />

</RelativeLayout>

I am developing using the Eclipse plugin, which does not show any errors and seems to run the application correctly in a simulator or on a real phone, but when I press the play button nothing happens. I'm not sure if the simulator supports sound (but I assume that it does), and I confirmed that the sound is muted on my phone.

What am I doing wrong?

, , , Eclipse, LogCat. , -?