Z4 2009 Radio won't start

Weird problem on a BMW Z4 2009:

Radio working fine, I turn it off (push on main button) as I go into underground garage,
Several hours later, retrieve car and drive out of said garage. Radio menu nowhere to be found, can't activate any audio (radio, cd, satellite etc)

Once home (above ground) I park car and remove key etc. On a hunch I reinsert key, radio , cd etc now work fine.

Rings a bell ?

Regards,

Pierre.

Theory that is not proven:
Logic7/Harman Kardon amplifier short-circuits/overheats/stuck at the booting up process. So the head unit responses to the buttons, but no audio is coming out the speakers, in my case not even park assist beeps while in reverse and backing up into a object. But I couldn't duplicate the problem for the dealership and they only replaced the head unit and reprogrammed the car. The problem came back in about 3-4month.

I have 2008 E92 335xi with Logic7/Harman Kardon

Check out this thread that I started on what could be the same type of problem.

http://www.bimmerfest.com/forums/arc.../t-599948.html

I have not taken it to the dealer yet to see if they can fix it.