“Hardware” is the circuit board, the microcircuits on the circuit board, the resistors, capacitors, inductors, connections, wires, antennas, battery, screen, camera, etc. There are over 1,000 parts inside an iPhone, and one or more of them may have failed. The phone can only be repaired by a qualified technician if there is a hardware failure.
Have you tried force restarting the phone?
- Press and quickly release VOLUME UP
then
- Press and quickly release VOLUME DOWN
then
- Hold the SIDE button until an Apple logo appears (15-30 seconds), ignoring "slide to power off" if it appears
The operative word here is QUICKLY; and try it a couple of times, the timing is a little tricky.