Why does home screen keep coming on?

try a hard reset.. home and power for 10 seconds until the apple appears then release the buttons and allow to reboot. if that doesn't work I'd open the phone when it is off (so the screen doesn't blow) and just check the home button prongs/connection for damage/aren't flattened and that the power button is fully responsive/connected properly at the motherboard. depending on where abouts the damage to your phone is will be more of a hint to you as to what might have been damaged..ie if it's near the power button it may be jammed in the "on" position hence the restarts.