What to do if phone suddenly displays a blue screen?

MY PHONE JUST GOES TO SOME BLUE SCREEN AND WONT LET ME DO ANYTHING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! WHAT  DID I DO?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?!?




Hi. What where you doing with your phone before the blue screen came up?



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