Currently Being ModeratedJul 26, 2013 11:47 AM (in response to Tiesto1975)
When you say that you can't turn on wifi, do you mean it is grayed out? Did the issue occur after a software update?
Have you looked at this article? http://support.apple.com/kb/ts1559
There are several LARGE discussions on this forum about this issue; take a look at them if you have some free time:
Currently Being ModeratedJul 26, 2013 12:08 PM (in response to Tiesto1975)
Almost always, the grayed out WiFi is a hardware failure that requires replacement, but try the steps in the article posted by Brandon first.
Don't try the "freezer" method you may read about in some threads. At best, this is a temporary fix and is likely to cause additional damage to the phone and void any remaining warranty.