Testing the diagnostics screen and accidentally hit the software update button. i could not get out of the screen and decided to turn off the car and disconnecting battery thinking the screen would go back to the normal menu. but when i turned the car back on the navigation screen did not turn on. non of the buttons on the pannel worked either, Only AC comes on.

 

You may be able to insert a newer DVD but otherwise will need to replace the unit. It's a disaster to do what you did.