The User Login Block is by default deactivated in most of our themes and can be activated if you wish through the block management region, in Drupal.
However, you can still log in through the login page at the following address: http://{installation_url}/user or http://{installation_url}/?q=user
For your convenience, here's an example of the PressBlog Playground login page http://playground.morethanthemes.com/drupal7/pressblog/user