To add to Bryan's post:

Hit 'SVC' > 'Aux' > Hold Mute, 1, 3 together for 5 seconds or so.

This is for a COMAND 2.0 system. Within that menu is a diagnostics where you can reset the system.

Good Luck

__________________
-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi