The rec nav radio screen has grey black and white lines and nothing else

My 2005 chrysler rec navigation started also going black 3 months ago, but every morning when its cool outside and i turn my car on the screen turns on and all the buttons work perfectly for 5 mins until it goes black again. I took it to a stereo specialist who said I need a new motherboard which cost same price as the navigation then tried selling me so ********* he had at his shop so he can make more profit. I know nothing about this navigation but enough about computers to assume its a faulty sensor or that my fan is just not working causing it overheat and sensor to quick in causing the screen to go black. My 2005 chrysler rec navigation started also going black 3 months ago, but every morning when its cool outside and i turn my car on the screen turns on and all the buttons work perfectly for 5 mins until it goes black again. I took it to a stereo specialist who said I need a new motherboard which cost same price as the navigation then tried selling me so ********* he had at his shop so he can make more profit. I know nothing about this navigation but enough about computers to assume its a faulty sensor or that my fan is just not working causing it overheat and sensor to quick in causing the screen to go black.