My large screen on the SAT NAV sits there flickering.

I have started the car up and moved it, the DISPLAY sometimes comes up with a basic text based screen in light blue, with no NAV computer.
If I hold my finger on the EJECT button permanently all is well, the 'BMW' logo comes up the graphics are correct, and the location is correct . The moment I let go of the eject but it start to reload and fails. The EJECT button does continuously flash!!

I occasionally get a basic light blue screen with no NAV computer. Any help would be appreciated.