Same thing happened to me in September. After trying a battery pull, cache wipe, and factory reset, the phone got sent back to Samsung. The motherboard was replaced. In my case, though, when the phone came back to me it couldn't be activated again on Sprint's network. It's back with Samsung, For The 4 the Time, now. I'm hoping they get it right finally. Since they replaced the motherboard the phone shows to Sprint as a Virgin Mobile device. Samsung keeps assuring me they will get it right the next time, and I keep sending it back to them - I know, that's insanity defined. Luckily I have a replacement S3 while this back and forth goes on, otherwise I'd be looking at buying a new phone before my contact term is up.
Let us know what happens with yours.
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