If you have forgotten your password to login on a BOINC project website, you would normally use the get_passwd.php webpage to send you an email containing a 1day link to reset your password.
If the project's mail server isn't up and running, you can use your account key as your password to login to most BOINC projects.
if you are already attached to the project, go to your BOINC data directory, open [...assosiated project...].xml with a text editor (ie: Notepad), copy the 32 character hexadecimal value between <authenticator></authenticator> and paste that into the password field on the login page along with the email address.
Forgot BOINC Project Password
Re: Forgot BOINC Project Password
If you use an account manager (BAM! etc.) you can retrieve your password from their website or your browser.