Tried all the apple suggestions and in the end asked O2 to look at it, they wanted to charge me £136!! I decided to change to a HTC one which is a much better phone. Anyway now I didn't need the iPhone 4s I tried a solution I saw on utube. Turn the phone off and wrap the phone in a cloth and put it in the freezer for 20 mins. Take it out and switch it on and you wont believe it but it now works, WiFi is on and connect to networks at home and at work. No idea why cooling the phone fixes it but who cares it's now for sale on eBay!!