Error when trying to access another screen using a Boot

Question

My problem is this, I have my main screen that contains a button to access another screen, the code I’m using to make this call is:

btRegister.setOnClickListener(new View.OnClickListener() {          
@Override
    public void onClick(View v) {
        setContentView(R.layout.activity_register);
    }
});

It turns out that inside this new screen(activity_register) i have several fields(Edittext) and two buttons, Register and Cleanse, the task of the button Register is that when pressed it collects the values of the fields(Edittext) and enter in the String, for this I am using the following code:

Part 1:

EditText etRegisterName,etRegisterSecondName,etRegisterAge,etRegisterEmail,etRegisterPhone;

Part 2:

name = etRegisterName.getText().toString();
secondname = etRegisterSecondName.getText().toString();
age = etRegisterAge.getText().toString();
email = etRegisterEmail.getText().toString();
phone = etRegisterPhone.getText().toString();

In short, my Mainactivy this way:

public class MainActivity extends ActionBarActivity {
    EditText etSearch;
    EditText etRegisterName,etRegisterSecondName,etRegisterAge,etRegisterEmail,etRegisterPhone;
    Button btSearch,btRegister,btRegisterFinish;

    String name, secondname, age, email, phone;

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

        etSearch = (EditText) findViewById(R.id.Search);
        btSearch = (Button) findViewById(R.id.Search_Button);
        btRegister = (Button) findViewById(R.id.Register_Button);
        btRegisterFinish = (Button) findViewById(R.id.btRegisterFinish);

        etRegisterName = (EditText) findViewById(R.id.etRegisterName);
        etRegisterSecondName = (EditText) findViewById(R.id.etRegisterSecondName);
        etRegisterAge = (EditText) findViewById(R.id.etRegisterAge);
        etRegisterEmail = (EditText) findViewById(R.id.etRegisterEmail);
        etRegisterPhone = (EditText) findViewById(R.id.etRegisterPhone);

        btSearch.setOnClickListener(new View.OnClickListener() {            
            @Override
            public void onClick(View v) {               
                String busca = etSearch.getText().toString();

                String tableTest = name+secondname+age+email+phone;

                String[][] table = {{"Rosana","De Oliveira","39","[email protected]","[phone]"},
                                    {"Jackson","De Almeida","15","[email protected]","(00) 6666-66666"}};

                for(int i=0;i < table.length;i++){
                    for(int j=0;j < table[i].length;j++){

                        if(busca.contains(table[i][j]) == true){                            
                            AlertDialog.Builder searchOK = new AlertDialog.Builder(MainActivity.this);
                            searchOK.setTitle("Busca Concluida");
                            searchOK.setMessage("Nome: " + table[i][0] + "\n" 
                                                + "Sobrenome: " + table[i][1] + "\n" 
                                                + "Idade: "  + table[i][2] + "\n" 
                                                + "E-mail: " + table[i][3] + "\n" 
                                                + "Telefone: " + table[i][4]);

                            searchOK.setNeutralButton("Fechar", null);
                            searchOK.show();
                        }

                    }
                }
            }
        });
        btRegister.setOnClickListener(new View.OnClickListener() {          
            @Override
            public void onClick(View v) {
                setContentView(R.layout.activity_register);
            }
        });
        btRegisterFinish.setOnClickListener(new View.OnClickListener() {            
            @Override
            public void onClick(View v) {
                name = etRegisterName.getText().toString();
                secondname = etRegisterSecondName.getText().toString();
                age = etRegisterAge.getText().toString();
                email = etRegisterEmail.getText().toString();
                phone = etRegisterPhone.getText().toString();

                AlertDialog.Builder confirmRegister = new AlertDialog.Builder(MainActivity.this);
                confirmRegister.setTitle("Dados do Registro:");
                confirmRegister.setMessage("Nome: " + name + "\n"
                                            + "Sobrenome: " + secondname + "\n"
                                            + "Idade: " + age + "\n"
                                            + "E-mail: " + email + "\n"
                                            + "Telefone: " + phone);
                confirmRegister.setNeutralButton("Alterar", null);
                confirmRegister.setPositiveButton("Registrar", new DialogInterface.OnClickListener() {                  
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        setContentView(R.layout.activity_main);

                        AlertDialog.Builder alertSucess = new AlertDialog.Builder(MainActivity.this);
                        alertSucess.setTitle("Registrado!");
                        alertSucess.setMessage("Registro feito com Sucesso!");
                        alertSucess.setNeutralButton("OK", null);
                    }
                });
                confirmRegister.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, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

My problem is that when I try to access this screen(activity_register) of error saying that the application has stopped! I can’t even access another screen where this button completes the Log, does anyone have any idea what it might be? if the question got confused I’m sorry, leave in the comments I will try to explain better!