Don't know if you still have that problem but I've come across a possible solution in an other forum
As my wife has had the same problem.
This is what was said and worked for a couple of people, I'll be trying it tonight and post the results within 24 hours.
(From other Forum):
Re: iphone4s will not turn off
30-Nov-2012 17:16 (in response to...)
Sounds like to me you are in "I got my iphone wet denial" haha...
Anyway, I had this problem once. My wife ended up putting a pair of pants in the washer that had my phone in it! Amazingly after i figured out where it was I found it was on. I tried to to turn it off but it just wouldn't stay off. I immediately went in settings to turn on airplane mode so I didn't receive any calls..
Since I don't have the replacement plan I kept the phone. My wife told me about a trick with rice (yes, rice. regular cooking rice) where you put your phone, or any electronic device for that matter in it and let it sit for about 24hrs. That will remove any water, or condensation from the internals of the device.
So, being the skeptic that I am I laughed and said "whatever".. Put my iphone in a sandwich bag, filled up the the bag about halfway with rice and let it sit over night.
Next morning phone turns off, stays off and problem resolved. My wife of course had to rub it in my face that it did work!
May, or may not work for you, hope it does.
Good luck.
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