Why won't my upload script work? No errors

My upload form is

<form action="accept-file.php" method="post" enctype="multipart/form-data">
Your Photo: <input type="file" name="photo" size="25" />
<input type="submit" name="submit" value="Submit" />
</form>

And accept-file.php is

<?php
error_reporting(E_ALL);
ini_set('display_errors', '1');

//if they DID upload a file...
if($_FILES['photo']['name'])
{
    //if no errors...
    if(!$_FILES['photo']['error'])
    {
        //now is the time to modify the future file name and validate the file
        $new_file_name = strtolower($_FILES['photo']['tmp_name']); //rename file
        if($_FILES['photo']['size'] > (1024000)) //can't be larger than 1 MB
        {
            $valid_file = false;
            $message = 'Oops!  Your file\'s size is to large.';
        }

        //if the file has passed the test
        if($valid_file)
        {
            //move it to where we want it to be
            move_uploaded_file($_FILES['photo']['tmp_name'], 'uploads/'.$new_file_name);
            $message = 'Congratulations!  Your file was accepted.';
        }
    }
    //if there is an error...
    else
    {
        //set that to be the returned message
        $message = 'Ooops!  Your upload triggered the following error:  '.$_FILES['photo']['error'];
    }
}

//you get the following information for each file:
$_FILES['field_name']['name']
$_FILES['field_name']['size']
$_FILES['field_name']['type']
$_FILES['field_name']['tmp_name']

?>

It is copied directly from a tutorial that apparently works ok. As you can see I've ever forced some error reporting at the top, but all I get when I submit the form is a blank screen (browser loads file-accept.php) and the uploaded file does not appear in uploads/ (chmoded to 777).

EDIT: I am now getting these errors:

Array ( [photo] => Array ( [name] => k3Jb9gv.jpg [type] => image/jpeg [tmp_name] => /tmp/phpzc4fLT [error] => 0 [size] => 384262 ) )

Notice: Undefined index: field_name in .............. on line 38, 39, 40, 41

This line gives you the problems:

$new_file_name = strtolower($_FILES['photo']['tmp_name']);

You should change that to something else like:

$new_file_name = strtolower($_FILES['photo']['name']);

This is because otherwise you filename is the whole temporary url of your file (including directories). That will give you a warning that you are not allowed to upload it there.

Also, you need to set $valid_file to true somewhere, probably before your check for the valid file.

//if they DID upload a file...
if($_FILES['photo']['name'])
{
    print_r($_FILES);
    //if no errors...
    if(!$_FILES['photo']['error'])
    {
        $valid_file = true;
        //now is the time to modify the future file name and validate the file
        $new_file_name = strtolower($_FILES['photo']['name']); //rename file
        if($_FILES['photo']['size'] > (1024000)) //can't be larger than 1 MB
        {
            $valid_file = false;
            $message = 'Oops!  Your file\'s size is to large.';
        }

        //if the file has passed the test
        if($valid_file)
        {
            //move it to where we want it to be
            move_uploaded_file($_FILES['photo']['tmp_name'], 'uploads/'.$new_file_name);
            $message = 'Congratulations!  Your file was accepted.';
        }
    }
    //if there is an error...
    else
    {
        //set that to be the returned message
        $message = 'Ooops!  Your upload triggered the following error:  '.$_FILES['photo']['error'];
    }
}