Check the following things :
Connection settings in Internet Explorer. Make sure that the LAN settings are set to automatic.
If this doesn't work, try a reset in Advanced Settings (assuming you are using IE7).
Check the TCP/IP settings for your wireless connection. Check they are both in auto mode.
Assuming you have installed you wireless cards software, try disconnecting the connection you have and reconnecting using the software (or, if you have connected using the software, disconnect and try connecting with the Windows native software).
Run the CMD command and type in ipconfig /all . This should show your wireless connection. The IP address should be 192.168.x.x If the first 2 sets of digits are different, then it isn't connecting properly.
That should keep you busy for 5 mins!