Is there a way to shut down YAHOO with out loosing my ATT email?

Oh that problem!   There's lot's of threads where legacy account users like you try to log into the att/yahoo webmail and end up at yahoo.  The first thing you need to try is to change your password (if you can).  One such place is Forgot ID/Password.  If you cannot change your password or even if you do but still have the same problem I suggest calling Digital Assistance Center (877-273-2728).

As for using email client apps, they might work but I suspect they won't until you get the account password working on the att/yahoo webmail.  But it's worth a try particularly when you read this page to get the proper email server settings you will see the recommendation to use a secure mail key instead of the password in the client.  Creating one of those and using it in the client means the client doesn't need the account password and thus (hopefully) bypasses the problems involving the it.

Even if this does work you still need to get the webmail login straightened out if for no other reason than you need to occasionally (less than a month) visit the webmail to check the spam folder for false positives (stuff marked as spam that really isn't spam).