Logged in but not able to do anything

Hi,

I'm new to this forum and rather new with drupal so I hope I make myself clear and that someone can help.
I've setup a new drupal site and I've been adding modules and edithing themes etc.
Everything semes to be working just fine.
I logged out to see how non-users see the site, nice of course.
Then I try to log in, with the adminster account, and...nothing.
I am logged in so I can see in the topic "who's online" but I cannot go to the adminster menu, not even through a direct url.
Through a direct url I get "Acces Denied", "You are not authorized to access this page.".

Can anyone help me. At first everything seems to be working fine but now I cannot even administer my own site!
I've been searching through different forums but I haven't found the answer.
Only that I maybe have to change te setting of the PHP server from CGI to ISAPI.
But my site is hosted and I don't have rights to change this.

Hope to hear from anyone.

Thanks.

Niels