Start car Nav screen comes on as normal all buttons function,and/or screen comes on then goes black and only info button and all buttons under map guide etc do not operate. ON AND OFF SPORATICALLY. PROBLEM FIX?

Hello, this is unfortunate, but it's not very possible to know what is happening with your navigation unit without hands on testing. You may require an automotive audio expert to help. It would appear that there is an internal issue with the navigation or audio unit, or the disc supplying the information, if it's one that remains loaded in the system.