WiFi does not work on iOS 6.1.1

I got a new iPhone 4S which had iOS 5.1.1 preloaded on it. When I tried to turn on WiFi, it was greyed out. The Store rep asked me to upgrade the OS. I have now upgraded to iOS 6.1.1. I can now seee WiFi on the first page but when I go to the second page, it is greyed out again. What do I need to do to get WiFi up and running again. Its frustrating.