What could be the reason?

I just bought 2002 model Rover 45 car and also bought an navigation system (TomTom). When I fitted TomTom and tried to charge from cigarette lighting point for the first time, the audio system became disable and nothing displays on its LCD. However, there is a flashing light from the audio system. I am not sure whether this is due to security system or something else. I have a security code, but can not enter as the LCD display is completely blank. Please advise me.