Can't connect to database after having published a new blog entry

Hi,

I just switched the server for my wordpress site.
Everything was working great, even uploading pictures.

I wrote a new blog post.
As soon as I published it, I got either an HTTP:500 error or a cannot connect to the database.

In wp-config.php,
/** MySQL hostname */
define(‘DB_HOST’, ‘localhost’);

I changed locahost with the ip address of the server, to no avail.

I really don’t know what’s going on, any help would be welcome.