If you are unable to see your team or league, please make sure you are logged into the NFL.com account with which you drafted the team. Many times users will draft a team while signed in with one username/email address and later sign in with a second email address and not be able to access the league.
If you have been signing in with your email address, try signing in with your username instead. If you've already been signing in with the username, try the email address.
Users without a password or access to the email account associated with an NFL.com account will not be able to access that NFL.com account. You may want to create a new NFL.com account with an email address for which you do have access.
In a custom fantasy league, the League Manager can use the Edit Team Owners tool to remove your old account and send an invitation to the email address associated with your new account at the same time.