(in the case that there's no outtage)
ping your gateway -and not just the default four packets.
"ping <gateway IP> -t"
Let it go for about a minute or two to get several hundred packets out.
If you're getting pings higher than 200, you'll get a truck roll.
If you're getting more than 2% packet loss, you'll get a truck roll (I believe).
If you've got a perfect connection to the gateway, AT&T won't do jack about anything else outside of their network.
reinstall NIC drivers?
reinstall TCP/IP?
power cycle modem (for a full three minutes)?
Good luck
nik