Unit seems dead - step by step:
 

For cars with CANBUS

First thing to test is power going into the stereo.
These stereos only need 3 things being
a) power on the Yellow wire
b) power on the Red Wire
c) earth on the Black

Using a multimeter /test light test if you have power on both the red and yellow when the engine is on.

If no
  check ALL fuses.  Unlike the old radio these units will travel through 2 fuses (normally the radio for
  accessories and another for a constant) and so all fuses need to be checked.

    If all fuses are ok replace the CANBUS module.  Please send a picture of the module

If yes
  Put the car in reverse and check for an image
    If you see the image you have a voltage leak at the back of the car - get this tested
    If you do not see an image the screen needs to be replaced.



For cars without CANBUS
First thing to test is power going into the stereo.
These stereos only need 3 things being
a) power on the Yellow wire
b) power on the Red Wire
c) earth on the Black

Using a multimeter /test light test if you have power on both the red and yellow when the engine is on.

If no
  check ALL fuses.  Unlike the old radio these units will travel through 2 fuses (normally the radio for
  accessories and another for a constant) and so all fuses need to be checked. 

   
If yes
  Put the car in reverse and check for an image
    If you see the image you have a voltage leak at the back of the car - get this tested
    If you do not see an image the screen needs to be replaced.