Wifi Failed on iOS 8.3 Upgrade
2 or 3 weeks ago, once I saw iOS 8.3 available, I upgraded my iPhone, and ever since my Wifi has turned off and refused to toggle and work! It's nasty!
iPhone 4S, iOS 8.3, White
Try the suggestions here to see if they resolve your problem:
http://support.apple.com/kb/ts1559
If those solutions don't work your iPhone 4s has probably developed a hardware problem. The permanent solution is to get it replaced.
You can search the internet for heating and freezing solutions that might work (at least for a while).
For example, see here: https://www.youtube.com/watch?v=nj10bz5bI6A
Root cause: On some iPhone 4s devices there may be a flow soldering problem with the WiFi chip. After long periods of WiFi activity such as installing an iOS update (for example, iOS 7 or iOS 8) there may be a connection failure. A work-around to this is the procedure in the youTube video.
A true hardware fix may be found here:
https://www.ifixit.com/Guide/How+to+Fix+iPhone+4S+Wi-Fi+Grayed+Out/22167