If you have forgotten your password please Go to Nokia Account web page https://account.nokia.com/acct/account/index.html and click on "Forgot your password?".
Make sure that you are typing the correct (Registered) email address, mobile number or Nokia Account username. After a short while you will receive a link to reset your password.
In case you did not receive the e-mail, make sure that your email inbox is not full i.e. you can receive emails normally from other parties.
In case you did not receive the link via SMS, make sure that your phone number must be preceded by "+" sign and the country code.
If the issue still persists, try to perform the previous steps using a different Internet Browser, PC or the internet provider.