Issues relating to a cracked or scratched phone screen, if you are having issues with your screen but your phone is not scratched please refer to the next section.
If your screen is cracked or heavily scratched it can effect the the function of the phone and may need to be replaced. If a scratch or crack is causing your device to malfunction it is most likely because the digitizer/LCD has been damaged. You can find a guide to replacing these here.
Issues relating to the screen not working properly or not responding to touch (this does not include cracked or scratched screen replacement).
If your phone turns on normally but will not respond to touch it is most likely an issue with the digitizer which will need to be replaced. The digitizer is attached to the front lens/LCD. A guide to replacing this section of the phone can be found here.
If you can hear your phone turning on but nothing is appearing on the display it is possible that you have a broken LCD which will need to be replaced. You can tell if it is a broken LCD rather than a broken digitizer based on whether or not your screen responds to touch.
External damage to the plastic frame or body of the device unrelated to specific components.
If the outer bezel of your device is cracked or broken it can be dangerous as your device normally is protected by it's plastic outer body. If the outer body of your phone is cracked or missing it should be replaced.
Issues related to the phone not powering on at all such as the power button, battery and charging port.
Over time batteries may lose their ability to hold a charge causing the phone to have an extremely short battery life before needing to be recharged. To fix this issue you can order a new battery online and replace the existing one.
If your phone does nothing when plugged into the charger or computer it is most likely an issue with the charging port being loose or needing to be replaced. If you have already confirmed that it is not an issue with the phone's battery you can replace the port easily as it is a separate part from the motherboard.