Try the following...

Go to Start > Run, and type in: cmd

At the Command Prompt type the following commands, one at a time, and press Enter after each:

Code:
ipconfig /release
ipconfig /renew
ipconfig /all
Check if your IP address returned to its original format (192.168.x.x)

You can also try resetting your router by holding the reset button on the back for about 30 seconds and then releasing. Give the router a few minutess to initialize itself and then attempt the connection again.
You also need to reset your wireless password (WPA, WEP) after your router is reset.

If still no-go, you may want to contact your ISP, or, post the connectivity problem in the following forum:
Network & Sharing - Windows 7 Help Forums