As in does not power on? Could be a fuse. Not giving your position? Not finding locations? Sorry but a description of "not working" just tells me it's broken. But in any case your best bet would be a shop that does car electronics, or the dealer. Although the dealer will either recommend replacing the whole unit or will sub it out to an electronics shop.
It tells me to install the DVD. The DVD is installed. I went to the dealer and one of the mechanics took me aside and told me he could replace it for less, on the side. What I don't understand is why a new DVD upgrade won't work. Should the GPS be failing like this? I was told that these units get overheated being in the trunk. If that were the case, why would the 2011 models still have the GPS system in the trunk?
I guess you have the "Please insert the navigation DVD" message.
There is a Navigation System Software Update out from Audi to fix this problem.
You need to take it to a dealer or to an independent Audi/VW shop who has OE diagnostic computer and get the new software loaded to your car.
Here is the TSB's # for reference:
91 08 180
December 17, 2008.
Supersedes Technical Service Bulletin Group 91 number 07-21 dated May 16, 2007