Sometimes this forum is useful, if only to know that you're not the only one suffering misery!
After pulling my car from winter storage everything worked fine. Three days later the radio buttons became unresponsive, now entire nav/radio is shut down, and no signal indicators either (the signals work outside the car, but no click or display on the dash). This is actually the second time it has happened to me, the first was after ten days of sitting. My solution then - after a Board search - was to disconnect the battery for an hour and let all systems "die", and reboot once reconnnected. That one worked. So, I try it again this time, as logic would dictate. However, no change. I'll keep looking in the meantime, but if anyone has a solution to suggest, I'd appreciate it.