A few things I've heard (including from customer services advisors) but not tried and may be old wives' tales:
1) Press Browse and Mute together and hold until the screen goes blank
OR
2) Put ignition on (but don't start engine), hold the green phone and voice recognition buttons on the steering wheel down together for 30 seconds.
Then: Let go of buttons, turn key off, and then open driver's door for 30 seconds. Close door, put key in ignition and turn on again.
OR
3) Press Radio, Media and Browse together for 5-8 seconds to enter "engineering menu" and see if there is an option for a system reset.
Nick