Trouble with the sign up

protected TextView mSignUpTextView;

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

    mSignUpTextView = (TextView)findViewById(R.id.signUpText);
    mSignUpTextView.setOnClickListener(new View.OnClickListener() {         
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent intent = new Intent(LoginActivity.this,
                            SignUpActivity.class);
            startActivity(intent);

        }
    });

    if (savedInstanceState == null) {
        getFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }

    }

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.login, 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);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_login,
                container, false);
        return rootView;
    }
}

<EditText
    android:id="@+id/usernameField"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:ems="10" 
    android:hint="@string/username_hint" >

    <requestFocus />
</EditText>

<EditText
    android:id="@+id/passwordField"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/usernameField"
    android:layout_below="@+id/usernameField"
    android:ems="10"
    android:inputType="textPassword" 
    android:hint="@string/password_hint"/>

<EditText
    android:id="@+id/emailField"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/passwordField"
    android:layout_below="@+id/passwordField"
    android:ems="10"
    android:inputType="textEmailAddress" 
    android:hint="@string/email_hint"/>

<Button
    android:id="@+id/signupButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/emailField"
    android:layout_below="@+id/emailField"
    android:text="@string/sign_up_button_label" />