If this is a fresh install of Wordpress then there should be no problems. How did you install Wordpress? One click install, manual, etc.. If you recently installed a plugin then that could be a cause. You may have to delete the plugin from the directory. Check to be sure the 'wp-admin' folder exists. Sometimes, the folder is moved into a different folder or not completely migrated.
This is just what I thought of in a few seconds. Read this blog post and look in the wordpress forums:
http://www.milessebesta.com/web-design/endless-wordpress-loop/