I just wanted to stop in to express my appreciation for your help. I never got around to posting my issue, but I spent considerable time reviewing this and other forums. Today, I have spent about 8 hours trying to figure out my issue. Finally, the answer was here: update the network adapter driver!
I have a Toshiba Satellite running Windows Vista Home Premium. Like another poster, I was able to connect to my AT&T U-verse Wi-Fi modem, but had no internet access. Access was possible with the ethernet. In addition, numerous devices in the house were connected with no problem.
As the computer is older (2007), the driver is old as well and had not been updated. Before reading about this possible solution, I had run a Microsoft "Fix It" for the DHCP; I had raised the power output to deal with a potential 802.11 issue; and I had struggled with the Network Location issue of not being able to make my wireless connection "Private," as it kept defaulting to "Public" mode (I was told this could be the issue). Once I updated the driver and connected wirelessly, the network connection switched to "Private" on its own, as I had set it.
I did exactly what Madhur suggested by going to the Devices section and clicking on "Update Driver" for my Atheros network adapter. The computer found the update on its own and installed it. Thanks in particular to Madhur!
Anyhow, thank you for your help. Hopefully, someone else with the same issue will be spared some suffering by reading this post. Cheers!