newbie, shut myself out of admin!

Hi, I have a huge problem!
I configured the blocks new to have the login displayed in the header section. But my theme ( altered changeme theme) apparently does not display it there. Now I cannot login again. I tried to access directly through the url www.mysite.com/drupal/?q=admin but it doesn't work. I get an access denied error.
What else is there to do? Could I temporarily switch to Garland theme?

Miriam