Iphone 4S ios 6.1 wifi problems

I got my iPhone with iOS 5.1.1, iOS updated to 6.0.1, WIFI became inactive, gray ... I waited for the update and released iOS 6.1 ... I was hoping to fix the error and still nothing, I tried to put my phone in the freezer, I've tried with the dryer and nothing, I do not know what else to do, I think it is not hardware problem, but not sure ... and menu General> About I have a MAC address on "Wi-Fi", help me please, I think the only way to fix this is to take where bought and exchange it, but wanted to solve ...