Assuming the retina display is not damaged, can you connect your device to iTunes and put it in recovery mode. You should see the following on your iPhone afterwards.
If you see can see that on your iPhone's retina display then you can assume the display is not damaged or faulty. From there, you may need to simply restore your device, either as new or from a backup. To put your device in recovery mode, follow the instructions below:
- Make sure you have the latest version of iTunes
- Plug your USB cable into your computer.
- Turn your iPhone off by holding the power button down until you see "slide to power off". Do as instructed.
- Now press and hold the Home button while reconnecting the USB cable to your iPhone. After iPhone is connected it should power on the device.
- Continue holding the Home button, you will see the Apple logo appear and then finally a "Connect to iTunes" will be displayed, now is the time to release the Home button. You will then see the following image:
Source: iPhone 101: How to Put the iPhone Into Recovery Mode | iMore
Assuming the retina display is not damaged, can you connect your device to iTunes and put it in recovery mode. You should see the following on your iPhone afterwards.
