No way to login, no fields where to enter any name/password

The Drupal install goes fine (congratulation message received...;o)), but now when I access my site and try to enter content or do administration I have always the message :
"Access denied
You are not authorized to access this page."
Probably I have to login somewhere but unfortunately I cannot find any form where I can enter usename/password.

Thanks for help
Gianfranco Oldani