A1 reverse parking sensors not working!!

[Bearxx]

Hi

 

Sorry if this question has been asked already!! When i select reverse or press the parking assist button i get a 3 second beep, in turn none of my sensors work and no image comes up on my display screen. I will see tonight if i can hear any noise from each sensor when parking assist is selected, however, i just wanted some help on what to do next! I'm trying to sell the car and can't really sell it with broken sensors!! 

Thank you in advance guys!