WP 2.8 (bug in admin style)

Hi,
I have problem with WP 2.8.
If I go to admin ( http://blog.rypi.cz/wp-admin/index.php ) I see only HTML(no CSS, no pictures…): http://easycaptures.com/5624336451

If I write after URL sometimes “?”, sometimes “?a” etc…, then all works good. This is very big problem.