unable to activate wifi

Does this describe your issue: WiFi Greyed Out

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 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