Has else had problem with wifi option being greyed out need to how to fix it

I recently updated my phone software to iOS 6.1.3 and for the first couple of weeks, it was ok. but then until monday, the option to turn on the wi-fi has been greyed out so I can't turn my phone's wi-fi on which means I have to keep using my 3G coverage which will eventually cost me a fortune if I don't get the wi-fi greyed out problem sorted out as soon as possible. If anybody could help me with this problem (without having to take it apart or putting it into the freezer) please let me know as soon as possible.

Thanks

alexmac92 x

:-)