It seems the file you are trying to install on your phone is not supported by your iphone that's why it shutdown,press and hold the power on button and menu button simultaneously for 30seconds,afterwards it reboots and comes on automatically,if it doesn't come on you will have to consult a qualified iphone technician to help you flash your iphone
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It seems the file you are trying to install on your phone is not supported by your iphone that's why it shutdown,press and hold the power on button and menu button simultaneously for 30seconds,afterwards it reboots and comes on automatically,if it doesn't come on you will have to consult a qualified iphone technician to help you flash your iphone