Welcome. Seems like you've just forgotten your admin ac
count data. There is no admin ac
count by default after installation.
YOU create it yourself right when you first try to login to admin panel.
So, if you really created an admin ac
count and now you can't log in (I understood you so), try to truncate a mysql table called
{your_prefix}_admins and then go to
http://www.openslaeditalia.helloweb.eu/admin.php. The system will ask you for creating a new admin ac
count. Create it and log in ;)
Also you may have changed admin-file name during your installation. Check it inside config/config.php ($admin_file variable). If there is something different from "admin" try to change it so it's equal to.
Good luck!