To log in to the site you first need to register. If you are already a registered Partyaner user and cannot log in, make sure you have entered all the login details correctly.
Make sure you have entered your e-mail and password correctly. Both data are case sensitive, so pay attention to lowercase and uppercase letters when entering e-mail and when entering a password.
If you have forgotten your password, then go through the "I forgot my password" procedure on the login home page to reset your password.