Greetings, my name is Justin and I will do my best to assist you with this issue.
First and foremost, ATT is your current service so you can contact them via phone support to request a password reset and check incoming email. However, if you're not testing your incoming email via WEB, and are trying to use a client software such as Windows Live Mail, or Microsoft Outlook, these are separate issues. You'll need to tell me which for me to assist further.
If you're not receiving email in your Web login here:https://login.yahoo.com/config/login_verify2?.partner=sbc
You need to test the above link. If you're using a mail client as previously stated, then let me know the software and we'll confirm settings from there.
As for contact recovery/mail recovery, this can be difficult. Yahoo is the hosting email (att goes through yahoo's servers).
The instructions for contact recovery are here:
At the bottom you'll see a contact form, click that, and fill it out. Give them time to attempt recovery.
As for email recovery, that's this link below, same process:http://tinyurl.com/d2j657b
There's a restore recovery form, same as the contacts form.
Let me know if you need any clarification and I will be happy to assist further. Once you are satisfied with my assistance on this matter please remember to return and rate the service I have provided (smiley's). Thank you, and good luck.