Please make sure that Site Address (URL) and WordPress Address (URL) are properly set.

I have kind of a huge problem though:

On www.domain.com I have prestashop, so that space was busy.

I therefor had already installed wordpress on:
www.domain.com/blog/

Today I enabled multisite, and I wanted to keep my blog on www.domain.com/blog. This works as before, BUT when I try to add another site, it automatically is created on www.domain.com/blog/blog2/
I want the new sites to be on:
www.domain.com/blog2 and so on.

I don’t want my primary blog address to be the “host” for the new sites.

As in: NOT www.domain.com/blog/blog2, but www.domain.com/blog2

It seems you might know your way around, so do you have any suggestions to fix this?

In my wpconfig I have now:

define(‘MULTISITE’, true);
define(‘SUBDOMAIN_INSTALL’, false);
define(‘DOMAIN_CURRENT_SITE’, ‘yourdomain.com’);
define(‘PATH_CURRENT_SITE’, ‘/blog’);
define(‘SITE_ID_CURRENT_SITE’, 1);
define(‘BLOG_ID_CURRENT_SITE’, 1);

I tried changing this to your example:
define(‘PATH_CURRENT_SITE’, ‘/’);

And the main blog and it’s admin still works, but not the network-admin.