From the login page there is a 'Forgot Your User Name' option, this is a good place to start to make sure you are using the correct username when you log in. Click on this link and input your registered email address and the system will send you an email with your registered user name.
Now you have your username try to log in again with the correct username. If you still can't log in then the next step is to reset your password. From the login page, there is a 'Forgot Your Password' option. Click on this link and input your registered email address, the system will send you an email so that you can reset your password.
When you reset your password the system will ask you to log in, from the login page it's important to clear any saved passwords and type in your new password that you just selected.