WordPress MU

I've upgraded wpMU 2.6.5 to wpMu 2.7 but sadly the subblogs shows 404 not found
I've done exactly like upgrade readme from
http://codex.wordpress.org/Upgrading_WPMU
could anyone tell me is something missing ?
thank you

Checked error log? Are you using subdir or subdomain install? Do ALL subblogs show 404?

thanks venture maker. I've checked the error_log but shows nothing. I'm using subdomain install and yes ALL subblogs show 404.
Even every pages that I created seems to be missing.
I've backup the database..
Am I supposed to be worry ?

Got .htaccess file? Show what's in it.
Got wp-config.php file? :) Show it too.

.htaccess is a blank file with 0 kb , opening it with notepad shows nothing
here's my wp-config

<?php

define( 'SECRET_KEY', '77nWD%f(0OJ5ImBm&fp)HgAG' );
define( 'SECRET_SALT', 'ePlYyhhKYe%RV2Ns8QchjaQ7' );
define( 'LOGGED_IN_KEY', 'S9X9SSUlARD&*1wp6Vbn8q#f' );
define( 'LOGGED_IN_SALT', 'YHh5yYaI7Exxz)sWW8e^WfYt' );
define( 'AUTH_KEY', 'nJAT@k$m2nAa5&5PW70Z%x*&' );
define( 'SECURE_AUTH_KEY', '2S&onbSahsduhkN%^QT95yx9' );
define( 'SECURE_AUTH_SALT', 'dSDRdfBce%Gs)R7XHvyc1Knj' );
define( 'NONCE_KEY', 'V)n3M9L#$6W78KOBOKfYk2zW' );
define( 'AUTH_SALT', 'A@dABcQibUz4@Xy8dUS@d7lU' );

/* Don't try to create this file by hand. Read the README.txt and run the installer. */
// ** MySQL settings ** //
define('DB_NAME', 'k37org_wp'); // The name of the database
define('DB_USER', 'k37org_mar'); // Your MySQL username
define('DB_PASSWORD', 'h4jim5'); // ...and password
define('DB_HOST', 'localhost'); // 99% chance you won't need to change this value
define('DB_CHARSET', 'utf8');
define('DB_COLLATE', '');
define('VHOST', 'no');
$base = '/';
define('DOMAIN_CURRENT_SITE', 'k37.org');
define('PATH_CURRENT_SITE', '/');
define('BLOGID_CURRENT_SITE', '1');

// double check $base
if( $base == 'BASE' )
die( 'Problem in wp-config.php - $base is set to BASE when it should be the path like "/" or "/blogs/"! Please fix it!' );
// You can have multiple installations in one database if you give each a unique prefix
$table_prefix = 'wp_'; // Only numbers, letters, and underscores please!

// Change this to localize WordPress. A corresponding MO file for the
// chosen language must be installed to wp-content/languages.
// For example, install de.mo to wp-content/languages and set WPLANG to 'de'
// to enable German language support.
define ('WPLANG', '');
// uncomment this to enable wp-content/sunrise.php support
//define( 'SUNRISE', 'on' );

define( "WP_USE_MULTIPLE_DB", false );

/* That's all, stop editing! Happy blogging. */

define('ABSPATH', dirname(__FILE__).'/');
require_once(ABSPATH.'wp-settings.php');
?>

and it turns out I'm using sub dir install
sorry for the mislead

".htaccess is a blank file with 0 kb"

That's you're problem then.

thanks andrea turned out there is something wrong with the htaccess that I saved. luckily I still have back up from previous upgrades.
Everything is working fine now ..
thank you