If the Siri trick fails, try turning the phone off then dunk it into lukewarm water and turn it on while submerged. Keep under water until Apple icon has been on screen for 15 seconds. If it doesn't work, or the Apple icon doesn't stay on for the full 15 seconds, try the process again. It's called a wet reset. It'll clear the PRAM cache from the solenoid boot disk and you'll be good to go.