The display says "Navigation not fitted". I thought the disk might of been missing and I bought one and when I try to put it in the DVD holder it wont open door and take DVD. Acts as if there is no power to unit. Maybe I'm doing something wrong? Is it common for the units to go bad? For all I know there already is a disk in the unit but maybe don't work? Maybe a hint on how to approach this issue? New to this Forum and LOVE IT!!