If you still get emails about matches and messages then your account is still active. If you don't then POF might have deactivated it.
In any case try requesting your password:
https://www.pof.com/getpassword.aspx
Submit only the email address that is assigned to your actual POF account. This will actually reset your password by by sending you an email with a link to visit to enter a new password.
Check you spam folder for the email. If you don't get an email from POF after this then most likely your account has been disabled or deactivated.