You can’t get your phone to turn on.
The battery could have run out of charge. Try plugging the phone in to the charger and turning it on again.
The battery itself could be malfunctioning. If plugging the phone into the charger has no effect, the battery may need to be replaced. A guide for replacing the battery can be found here.
The display could be broken if you are sure the phone is on and you still don’t see anything. It may need to be replaced. A guide to replacing the display can be found here.
The motherboard could be damaged and may need replacing. A guide to replacing the motherboard can be found here.
You can’t hear calls, ringtones, or button sounds.
Check to make sure the phone is not on mute or vibrate.
Check the phone settings to see if the keypad sounds are turned off.
People cannot hear you speaking during calls.
Check to make sure that the microphone volume is not muted.
The microphone could be broken if the microphone volume is not muted. It may need to be replaced. A guide to replacing the microphone can be found here.
Your phone is not responding to button presses.
The keypad could be damaged and may need replacing. A guide to replacing the motherboard can be found here.