Inspiron 1420 (Vista) won't connect to Internet

Hello. I'm stumped and hope someone out there can help. Here's my story:
We had been using a USB internet connector on both our Dell laptop and desktop (both have Windows Vista) for about a year--with no problems. A few days after going wireless with AT&T, I uninstalled the usb program from the desktop because I got tired of it popping up. Well, that's when wireless stopped working on my desktop.  So we've been using the laptop for the past week for internet. The first few days we'd get instant wireless connection. Then, all of a sudden, a message would pop up saying we couldn't connect. After I'd diagnose the problem and find the connection, however, we would be able to get online. But I figured the problem was stemming from the fact that that we still had the USB internet connector installed on the laptop. So silly me, I figured if I uninstalled that program, I'd be able to get online with my wireless more quickly. WRONG!!!!! If only I could turn back the hands of time.

Once I uninstalled the usb program, I could no longer get online at all. The diagnostics tell me to plug a cable into the network adapter (what cable?), automatically get ip settings (that didn't work), reboot (didn't work either). Nothing works! I had an AT&T tech out here who looked at my desktop, and he said my IP address wasn't showing up or communicating. He was stomped. I was on the phone with another AT&T rep for two hours the other day when the laptop stopped connecting. She said she was stomped and had exhausted every troubleshooting possibility. Finally, she said it was also an IP address and/or driver issue that resulted when I uninstalled the connector from the computers. I know the AT&T modem/router is working properly, because I'm able to use it on my work laptop with no problem. It's the only computer in the house that we had never installed or used the USB internet connector on. Same thing when the tech was here installing wireless internet. He was able to connect wirelessly on his laptop. The problem is clearly with the computers that I uninstalled the usb programs. Dell tech support wouldn't help me because my warranties have expired (my computers are less than two years old).

Do I need to reinstall software or drivers? If so, which ones? And how do I do that? Please help!