Sound only plays once

[Wilson Cash]

Hi!

I was making an app for the android, where if you press a button, a sound plays. The problem is, that after playing one sound, pressing the buttons again does nothing

public class MainActivity extends Activity {

	Button s1, s2, s3, s4;
	MediaPlayer ss1, ss2, ss3, ss4;
		
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.linear);	
		
		s1 = (Button) findViewById(R.id.s1);
		s2 = (Button) findViewById(R.id.s2);
		s3 = (Button) findViewById(R.id.s3);
		s4 = (Button) findViewById(R.id.s4);
		
		s1.setOnClickListener(new View.OnClickListener(){
			
			public void onClick(View v){
				ss1 = MediaPlayer.create(MainActivity.this, R.raw.sound1);
				ss1.start();
			}
		});
		
		s2.setOnClickListener(new View.OnClickListener(){
			
			public void onClick(View v){
				ss2 = MediaPlayer.create(MainActivity.this, R.raw.sound2);
				ss2.start();
			}
		});
		
		s3.setOnClickListener(new View.OnClickListener(){
			
			public void onClick(View v){
				ss3 = MediaPlayer.create(MainActivity.this, R.raw.sound3);
				ss3.start();
			}
		});
		
		s4.setOnClickListener(new View.OnClickListener(){
			
			public void onClick(View v){
				ss4 = MediaPlayer.create(MainActivity.this, R.raw.sound4);
				ss4.start();
			}
		});
		
		
		
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}

How can I fix this?

Thanks!