what is noc (sp?)

For clarity; he is using YOUR PC and keying in HIS username into your DSL modem with no other changes?

Are you getting login/authentication failure messages? With his account logged in, can you go to bellsouth.net and check your webmail account?

It sounds like it could be a problem with your userid/password; their B-RAS won't hand out an IP without a good authentication and you can't surf without a good IP.

A BellSouth tech should have a way to escalate into their NOC - demand this if it is not offered.