Did you use your Facebook account to register? If you did, you will need to click on the 'Login with Facebook' button. If you are certain you used a particular username and password during registration but can't remember what password you chose, click on ‘Forgot Password’ on the login page. You’ll be prompted to fill out your registered email address. An email will then to be sent to you with a link to a page on the website where you can set a new password.
Don't forget - if you used your Facebook, resetting your password won't answer your problems. Please make sure your computer isn't logged into someone else's Facebook account when trying to login to Steptember!