WordPress MU

I have a site [ http://mynation.net ] with 5 subblogs hosted with wordpress mu 2.6.5
Main site and Blogs works fine but main site admin section is dosen`t allow me to do anything or shows like fresh instal.

it shows no users when there are many
Shows no blogs when there are many
Plugin directory disapeard but all plugins works fine
sub blogs allow to do everything but main blog not.
most of the time main blog take long time to load and fails to show anything.

Anyone faced such Problem ?

So, what's in your error logs?

its not creating any error_log file, before any system problem or php failure it used to create in base Directory.

is there any way to create error_logs on fly

I asked the web host, they said site works fine that means there is no problem with the system.

but from wordpress script side there is no update or new plugin install/update.

and i cann`t say wordpress problem, coz sub blogs r work fine. Problem only with ADMIN blog