Notification wird nicht angezeigt

import android.app.AlarmManager;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.os.IBinder;
import android.support.v4.app.NotificationCompat;

public class NotificationService extends Service {
	private static int num_msg = 0;
	public static void incNumMsg() {
		num_msg++;
	}
    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }	 
    @Override
    public void onCreate() {
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // Query the database and show alarm if it applies
    	Datenbank.getInstance().update();
    	int tmp = Datenbank.getInstance().getNumOfMessagesForUser(Datenbank.getInstance().getMyID());
    	System.out.println("Service meldet: "+tmp);
		NotificationCompat.Builder builder =
	            new NotificationCompat.Builder(this)
	                    .setContentTitle("My Notification Title")
	                    .setContentText("Something interesting happened");
	    int NOTIFICATION_ID = 12345;

	    Intent targetIntent = new Intent(this, TargetActivity.class);
	    PendingIntent contentIntent = PendingIntent.getActivity(this, 0, targetIntent, PendingIntent.FLAG_UPDATE_CURRENT);
	    builder.setContentIntent(contentIntent);
	    NotificationManager nManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
	    nManager.notify(NOTIFICATION_ID, builder.build());
		
	
        // I don't want this service to stay in memory, so I stop it
        // immediately after doing what I wanted it to do.
        stopSelf();

        return Service.START_STICKY;
    }
    @Override
    public void onDestroy() {
        // I want to restart this service again in one hour
        AlarmManager alarm = (AlarmManager)getSystemService(ALARM_SERVICE);
        alarm.set(
            AlarmManager.RTC,
            System.currentTimeMillis() + (1000 * 5),
            PendingIntent.getService(this, 0, new Intent(this, NotificationService.class), 0)
        );
    }
}

  NotificationCompat.Builder builder =
                new NotificationCompat.Builder(this)
                        .setSmallIcon(R.drawable.ic_launcher)
                        .setContentTitle(title)
                        .setContentText(message)
                        .setOngoing(true)
                        .setAutoCancel(false);