Re: my iPhone just randomly shut off and i hear siri but its a black screen what should i do
Firstly, I would hold down the power button and the home button until you see the Apple logo.
If that doesn't work, connect it to iTunes and see what you can get from that. It may be that you might have to restore it as a new device through iTunes.
I know someoe who had this issue and she rectified it with a quick reset by holding the buttons, as above.