WordPress MU

I have W-Mu 2.3.3 [ http://mynation.net ]
I have 5 subdirectory blogs

Yesterday i upgraded to mu 2.7.

STEPS DONE

Disabled all plugins of main site [ http://mynation.net ]
Renamed old wp-admin and wp-include as wp-admin-old and wp-include-old
uploaded new wp-admin and wp-include
Replaced wp-contents files (blogs.php, index.php)
updated all main files in /
Run admin/upgrade.php
After login, i updated all blogs
it updated all blogs without any errors
Main site works fine.
but when i click on blogs in admin panel it shows no blogs
nor all it shows any directory blogs eg http://mynation.net/abio/

i checked all possible settings, still no luck.

then i renamed 2.7 new wp-admin and wp-include to wp-admin-new and wp-include-new
and
wp-admin-old and wp-include-old to new wp-admin and wp-include
to revert back to 2.3.3 and old site works fine.

any expert on this problem ? why subdirectory blogs are not working.

Sure you have VHOST set the same as before in your wp-config?

THANK YOU;
I HAVE LIKE THIS.
hope this setting is correct one

define('DB_COLLATE', '');
define('VHOST', 'yes');
$base = '/';
define('DOMAIN_CURRENT_SITE', 'mynation.net' );
define('PATH_CURRENT_SITE', '/' );
define('BLOGID_CURRENT_SITE', '1' );