Reset Nav/Radio/Phone system?

Nav/Radio/Phone head unit just went dead middle of nowhere???

Just middle of nowhere... when a call comes in, I tried to answer and "I think" I press a wrong button, instead of the screen, I think I pressed the Phone button on the right side of the unit. Now, the whole head unit (Radio/Phone/Nav) went dark. When I left the Prius parked for few hours and I even removed the battery cable from the 12V battery on the rear right trunk but still no luck.

Beside the battery in the rear right side of the tunk, where else I can disconnect the battery cable and give that a try?

Anyone have any clue, how to fix or reset the head unit? Please advice. Thanks in advance.

 

Please help. Thanks!