I’ve got the “connection error” often when in admin panel

I’ve got a “Error establishing a database connection” problem when i’ve just posted an article or when i’m writing for too much time an article.

I’ve tried to optimise the mysql instance configuration and re installed twice both PHP and MySQL.

I’m seeking for someone that could have been facing this problem too to understand what cause it.

WordPress is running on :
. Windows Server 2003 x64
. IIS 6 with PHP 5
. MySQL 5.1

WordPress is running with :
. Askimet
. Google XML Sitemaps
. List Authors Plus
. SidePosts Widget
. Simple:Press Forum
. Twitter Tools
. WP-Mail-SMTP
. WP-Polls
. WP-PageNavi
. WP-UserOnline Widget
. WP-Wall