PRé sends you the original login credentials but these need to be changed the first time you login to the ecoinvent website. If these have been changed by someone from your end, and if you are not sure what the password is anymore, click on 'Forgot your password?'. Your password will be reset and a new one will be sent to your email address.
Another possibility may be the web browser. If you are constantly being redirected to the startpage, you may be using an old version of the Internet Explorer. Try updating your Internet Explorer to the latest version 11. Another option would be to use another browser like Firefox or Chrome.
If both suggestions do not work, please contact ecoinvent support directly at firstname.lastname@example.org.