Several users have reported Wi-Fi problems after updating to iOS 6. Many users say that their WiFi option is grayed out.
It seems that this bug was a result of Apple’s servers being down for a short time. Apple fixed this particular bug, so you do not need to do anything. If you are still having this issue, please leave a comment here.
Unfortunately, it seems that many users are still having this Wi-Fi disabled problem
- Reset network settings (General->Reset->Reset Network Settings)
- Toggle Airplane Mode on/off
- Restart your device
- Turn off Cellular Data ( Settings > General > Cellular) then try to connect to your WiFi.