nav screen goes blank
 

Hi, My BMW E46 sat/nav screen with the mark 3 computer has started getting a boarder round the maps and on the onboard computer screen it is if the screen is shrinking.it used to covered the hole screen, and also the screen is blank with only the date and time along the bottom when the weather is cold with frost on the car, then when the car heats up the sat/nav, onboard screen comes back, as anyone else had this happen to their sat/nav screen.