We are aware of issues some users are having with logging into Yahoo accounts and are working to fix this as quickly as possible.

Reasons Yahoo deactivates or deletes an account

Depending on your account's history, it's possible for it to be removed from Yahoo and become inaccessible. You can always sign up for a new Yahoo Account, but keep in mind that your old Yahoo ID won't be available for you to use. These actions can result in an account being deleted: