hey, i had the same problem. it's some kind of bug.
here is my fix (sorry im late with it)
open sd/sim slot.
with a tooth pick or something not too sharp press the reset button.
phone shuts down. u can restart it normally from the power button now. (NOTE: nothing will be delete; the button only forces the phone to shut down.)
= no need t take to service or provider....unless it happens more than once (only happened to me once so...)
Good Luck!
