After successful installation, nothing happend... why?!

I installed with success Gallery 3, but after click on the "Start using Gallery now". nothing happend. Only white page. No error ...

I try http://mywebsite/gallery3/index.php and nothing again... white page

This index.php looks like this:

<?php
/**
* Gallery - a web based photo album viewer and editor
* Copyright (C) 2000-2011 Bharat Mediratta
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.
*/
// Set this to true to disable demo/debugging controllers
define("IN_PRODUCTION", true);

// Gallery requires PHP 5.2+
version_compare(PHP_VERSION, "5.2.3", "<") and
exit("Gallery requires PHP 5.2.3 or newer (you're using " . PHP_VERSION . ")");

// Gallery requires short_tags to be on
!ini_get("short_open_tag") and exit("Gallery requires short_open_tag to be on.");

// Suppress errors. For information on how to debug Gallery 3, see:
// http://codex.gallery2.org/Gallery3:FAQ#How_do_I_see_debug_information.3F
error_reporting(0);

// Disabling display_errors will effectively disable Kohana error display
// and logging. You can turn off Kohana errors in application/config/config.php
ini_set("display_errors", false);

// Turn off session.use_trans_sid -- that feature attempts to inject session ids
// into generated URLs and forms, but it doesn't interoperate will with Gallery's
// Ajax code.
ini_set("session.use_trans_sid", false);

define("EXT", ".php");
define("DOCROOT", getcwd() . "/");
define("KOHANA", "index.php");

// If the front controller is a symlink, change to the real docroot
is_link(basename(__FILE__)) and chdir(dirname(realpath(__FILE__)));

// Define application and system paths
define("APPPATH", realpath("application") . "/");
define("MODPATH", realpath("modules") . "/");
define("THEMEPATH", realpath("themes") . "/");
define("SYSPATH", realpath("system") . "/");

// We only accept a few controllers on the command line
if (PHP_SAPI == "cli") {
switch ($arg_1 = $_SERVER["argv"][1]) {
case "install":
include("installer/index.php");
exit(0);
case "upgrade":
case "package":
$_SERVER["argv"] = array("index.php", "{$arg_1}r/$arg_1");
define("TEST_MODE", 0);
define("VARPATH", realpath("var") . "/");
break;

case "test":
array_splice($_SERVER["argv"], 1, 1, "gallery_unit_test");
define("TEST_MODE", 1);
if (!is_dir("test/var")) {
@mkdir("test/var", 0777, true);
@mkdir("test/var/logs", 0777, true);
}
@copy("var/database.php", "test/var/database.php");
define("VARPATH", realpath("test/var") . "/");
break;

default:
print "To install:\n";
print " php index.php install -d database -h host -u user -p password -x table_prefix \n\n";
print "To upgrade:\n";
print " php index.php upgrade\n\n";
print "Developer-only features:\n";
print " ** CAUTION! THESE FEATURES -WILL- DAMAGE YOUR INSTALL **\n";
print " php index.php package # create new installer files\n";
print " php index.php test # run unit tests\n";
exit(1);
}
} else {
define("TEST_MODE", 0);
define("VARPATH", realpath("var") . "/");
}
define("TMPPATH", VARPATH . "/tmp/");

if (file_exists("local.php")) {
include("local.php");
}

// Initialize.
require APPPATH . "Bootstrap" . EXT;

It's original file.
The tables in databases are created....

So, what can I do, please?!!