Welcome to the forum,

I agree with Douglas, the people that fitted the battery/alternator did not perform the power down procedure correctly for the MK3 (2001, I'll asume thats what you have).

As a result the Mk3 nav computer has failed and is now probably unrecoverable.

I would say that all you need is a new (or 2nd hand) Nav computer, your best be would be to get a replacement mk3 (or better, a MK4) and go from there (try ebay, they are approx $200/$300 for the mk3 and $500/$700 for the mk4).

Do you have the TV option (probably not as this would have taken over from the nav computer when it failed).

The long and short of it is that they screwed up, they should be getting it fixed that their cost because they did not power the nav computer down properly, they have caused the failure by just disconnecting the battery.

HTH

BTW

1: $2200 for the nav computer is way way too much...
2: The display sounds OK, its just the nav computer thats broken, get a 2nd hand replacement and go from there.

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Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.