My just over a year old iphone 4S stopped connecting to wifi. It started by not keeping the connection for very long. I would reset Network settings and that worked for a couple of weeks. Suddenly the actual blue slider bar won't even allow me to turn the wifi to "on" period!! I tried to erase and restore my phone but nothing. Had to manually install all my apps as iCloud won't connect as I need wifi! Help please!!!
Since it still fails after Restore, the iPhone WiFi chip or its solder connections to the logic board are faulty. There is no fix. If there is Warranty or AppleCare make Genius reservation or set up service and take or send to Apple for resolution.