Navigation System controls display?

[2001_White_X5]

Hello,

Our alternator and battery were recently replaced. Afterwards, the display is blank and the radio will turn off after a few minutes.

The shop says that the nav system is getting a signal but not pushing the data out. The display is completely dark but will flash every so often. The information on the instrument panel is default and does not show date or time. We have been told that everything goes through the nav system and without a new nav system, the display will never reappear.

Is this true? It seems unlikely as there are many X5's out there without the nav system. If it is, how can we fix it? They want $2200 for a new nav system and then $1100 to work on the display.

Any help, explanations, advice is appreciated!