After upgrading to Windows 8, I got the following error:
wifi doesn't have a valid IP configuration
I switched the Wifi settings from AES to TKIP and it started to work! If you can't get the wifi working on Windows 8, go to Start > control Panel (show small icons) > network and sharing center > click (on left) wireless networks > right click your network > properties.
Select Security Tab, and change the type to AES from TKIP, and click okay.
If you don't use AES settings, you may still want to change it to any other setting and see if it works.