There are certain guidelines that help to reactivate Yahoo account. This can be only possible if the Yahoo has been signing in within 12 months at least once from the deactivation time.
Visit the Yahoo sign page.
Provide the login details of deactivated account.
Click to confirm ID.
Attention: "role based name" email prefixes such as support, webmaster, info, contact, forum, service, affiliate, admin, traffic, partners, marketing, etc., for our member accounts are not permitted. They are acceptable for a vendor listing, but not for the member email. This is due to bulk email processors scrubbing them for delivery due to extremely high bounce rates. Please apply for membership using a personalized email prefix. Something like firstname.lastname@example.org.
If we discover you signed up with a role based name we will give you only one message to change it. After 3 days your account will be removed if the email is not changed.