My iPhone 4s won't let me turn my wifi on?

I've had my iPhone for a while now (longer than a year I think) and I haven't had any trouble with it before but my wifi was playing up yesterday so I turned it off and I tried to turn it back on and it greyed out so I can't even turn it on anymore. I've had a look on the internet to see about other people having the same problem and a lot of people have been saying it's because of the iOS6 update but I've had the update for a while so I'm not sure what it could be.

I've tried turning it off and on again multiple times and resetting my network settings and I've done a reboot by holding down the home button and sleep button, but nothing seems to be working. Does anyone have any ideas on what I should do to get it working again? Thanks.

Restore in itunes

"Try the following:
- A reset. Nothing is lost
Reset iPod touch: Hold down the On/Off button and the Home button at the same time for at
least ten seconds, until the Apple logo appears.
- Reset network settings: Settings>General>Reset>Reset>Network Settings
- Restore from backup
- Restore to factory settings."
I can't promise it will work. Back up your iPhone through iTunes, then disconnect the phone and turn it off. Hold down home and use USB to connect to your computer and put it into recovery. Restore through iTunes, but don't go to your backup until after using the setup wizard. At this stage it should reestablish WiFi. If not… Either way, then restore from iTunes, hopefully with functioning WiFi. Good luck!