Drupal 7 prevents brute force attacks on accounts. It does so by refusing login attempts when more than 5 attempts failed. The amount of failed logins is recorded in the table 'flood'. You can either wait before trying to login again or clean the flood table with one of the procedures below:
1.Manually delete all of (or the last applicable) rows in 'flood' table; or
2.Execute the following query on the Drupal database:
DELETE FROM `flood`;
or
To execute this query it will be necessary to login to the database. This is typically done through the command line or through a GUI interface such as phpMyAdmin.
3.From the command line, with drush installed:
drush php-eval 'db_query("DELETE FROM `flood`");'