MapFragment problems. This is all in white, and I can not make it display a map (ANDROID)

First of all, sorry for my English. The problem is I can not display a map in MapFrament. Seek help tutorials, and I could not fix it. I'm using the ADT adroind. I could get my key in GoogleDeveloperConsole. The problem is that when I run it explodes.

when you put these lines in the Manifest.xml not explode, but shows me the blank MapFragment:

      <meta-data
        android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version" />

I tried with all I had at my disposal, I need help. I leave my code.

Manifest.xml:

      <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://ift.tt/nIICcg"
    package="com.example.mapa"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

    <permission
        android:name="com.example.googlemaps.permission.MAPS_RECEIVE"
        android:protectionLevel="signature" />

    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true" />

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <!--
     The following two permissions are not required to use
     Google Maps Android API v2, but are recommended.
    -->
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.android.mapexample.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <meta-data
            android:name="com.google.android.maps.v2.API_KEY"
            android:value="MY KEY" />
    </application>

</manifest>

Activity.java:

package com.example.android.mapexample;
import com.example.mapa.R;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;

import android.support.v7.app.ActionBarActivity;
import android.annotation.SuppressLint;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

    public class MainActivity extends ActionBarActivity
    {

        static final LatLng TutorialsPoint = new LatLng(21 , 57);
        private GoogleMap googleMap;

      @SuppressLint("NewApi")
      @Override
      protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      try { 
            if (googleMap == null) {
               googleMap `=((MapFragment)getFragmentManager().findFragmentById(R.id.mapa)).getMap();`
            }
         googleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
         Marker TP = googleMap.addMarker(new MarkerOptions().
         position(TutorialsPoint).title("TutorialsPoint"));

      } catch (Exception e) {
         e.printStackTrace();
      }

   }

@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);
}}

activity.xml

    <RelativeLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:tools="http://ift.tt/LrGmb4"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.android.mapexample.MainActivity" >

    <fragment
      android:id="@+id/mapa"
      android:name="com.google.android.gms.maps.MapFragment"
      android:layout_width="matcenter code hereh_parent"
      android:layout_height="match_parent"/>

</RelativeLayout>

in theory the library was loaded successfully the project.

Could someone help me? please

Greetings