2nd layout Button is not working

This is my First Question & I'm a new android learner,

Suddenly in my ellipse 2nd layout button is not working; after pressing button of my first layout it working & going to second layout.

But in 2nd layout my Button is not working, I tested it very simple code. Please check

public class MainActivity extends Activity {
Button b1,b2;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    b1 = (Button) findViewById(R.id.button1);
    b2 = (Button) findViewById(R.id.button2);

    b1.setOnClickListener(new Button.OnClickListener(){

        @Override
        public void onClick(View v) {
            setContentView(R.layout.activity_main_activity2);               
        }

    });
}

@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;
}

}

This is my 2nd activity code

public class MainActivity2 extends Activity {
EditText ed;
Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_activity2);
    ed = (EditText) findViewById(R.id.editText1);
    button = (Button) findViewById(R.id.button21);

    button.setOnClickListener(new Button.OnClickListener(){

        @Override
        public void onClick(View v) {
            Toast.makeText(getBaseContext(), "Working", Toast.LENGTH_SHORT).show();         
        }

    });
}

@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_activity2, menu);
    return true;
}

}