That's what I would try first using the same USB stick and the stuff that's already on it.
Do you have the satnav menus, or is it completely borked. If not and you happen to have another stick, try the update from scratch (put it in your PC and do the map update thing) on the alternate USB stick. Don't use the existing stick, as it has the files that are needed from the satnav on it. (Preserve what you have).
Its this thing, you can choose in dashboard, not in HeadUnit. Its like compass. showing directions. so you dont need to look at the big screen, but just in front of you. under the speed. Everything else working like it should.