Hi there, I am Cris and will be glad to assist you.
Try pressing the top button and home button down together, continue to hold until the iPhone shuts off and the Apple logo appears.
When it does let go and wait for it to boot up.
Let me know if this works for you or we have to do further troubleshooting.
Yes sorry press the side button sleep/wake and the home down together at the same time until the apple logo appears.
How did it go?
Were you able to restart the phone?