When the alternative e-mail is locked, and there is no other recovery method available, a user will lose its e-mail account. The security question is essential to account recovery when it's about Yahoo. If you don't know the answer or have access to other recovery methods, then you will not be able to use the account anymore.
If you know the ID and password and tried to enter but you've received errors, it means your account is locked. You'll need to wait approximately 24 hours before you can actually log in again.