Range Rover navigation and radio problem

[Rangeroverkell]

Hello, i have a range rover 03 and the problem is whenever i turn the car on the navigation is blank and a black screen, and the radio will turn on and everything works for 1 minute after 1 minute the radio turns off and i have to turn on and off the radio for it to come back on. I tried disconnecting the battery and i have tried changing the navigation monitor non of these seem to work. Does anyone have an idea of how to fix this? Thanks for your help.