Gen 4 Sat Nav+Audio Unit won't switch on

[Monster]

I left my car at the paint shop to respray all sides of the car, however when I went to collect the car, I found that both the sat nav screen and the audio unit won't turn on, and the hazard lights were flashing. The workshop said all they have done was to remove the headlights and tail lights. Apparently they had some problems with the car alarm before (dealer fitted unit). Can someone tell me what is the cause of this issue and how can it be fixed?


Thanks.