Like Kurt said, try bypassing the wireless to see if you can get online. That lets you know that your Internet Service Provider is up (which ours - Charter - seldom is lately).
Click Start, then Run, then type cmd, then OK, then type ping
216.109.118.70 (or some other IP address). If you get replies, it means that your ISP is working.
If it's funky, do a power cycle. Shut down your laptop, unplug the wireless and the modem, wait three minutes (that's a subject of debate), re-power your modem, then see if you can get online directly through your modem. If you can, reconnect your wireless, and try it.
If the wireless still doesn't work, click Start, then My Network Places, then View Network Connections, then right-click on Wireless Network Connection, then click Repair, and wait for it to go through the repair process.
If that doesn't help, click Start, then My Computer, then View System Information, click the Hardware tab, click the Device Manager button. Anything that's having problems will be expanded (highlighted).
If that doesn't work, go to youtube.com and search for the video of the Harry Potter spell that you can cast on your computer to get connectivity. Just kidding.
I deal with this many times a day. I am so sick of playing these games. It's not a wireless card problem for me because at work, I never have a problem. The ISP tried to blame our wireless, but after visiting the house ten times, they realized that we were having, like, 900 disconnects in twenty minutes. It's still not right, but I am really tired of dealing with them, and I have more pressing issues at our house right now.
Disclaimer: this is not in my area of expertise, but I have watched these so-called experts doing this so many times that I am familiar with their tricks. I'm convinced that it's all voodoo magic.