Do you have a qualifying paid subscription to Creative Cloud? Unlike Behance which is free to everyone, you must be a Creative Cloud subscriber to use Portfolio.
If your username and password changed recently, contact Portfolio support team and ask them to move your Portfolio to the new account.
-- Contact Portfolio Support for technical help - https://help.myportfolio.com/hc/en-us/requests/new?ticket_form_id=177168
Nancy O'Shea, Product User & Community Expert
Alt-Web Design & Publishing ~ Web : Print : Graphics : Media