The Nav system controls all display on the bordmonitor, but has little to do with the gauge cluster.

It sounds like you are referring to your monitor up front, in which case, the most likely cause of no/bad display (in order of likelihood) are:
1. Weak battery
2. improper wiring of the nav unit
3. bad nav unit

If you had someone change out your battery / alternator there is a good chance that they didn't wait for the nav unit to power down before disconnecting the battery - this is a known cause of blown nav units.

d-

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.

__________________
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.

100% ditto with ccfj1's diagnosis.

Based on the year of your car, you probably have the MKIII navigation computer. Those are vulnerable to power loss. The most common cause of MKIII failure is any work on the electrical system, or a drained battery. You are in the market for a new nav computer. I would upgrade to a MKIV, as those units are bullet proof, and the extra features are sweet.

__________________
SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input

Thanks everyone! The alternator and battery went down together and left the car powerless. It also gave the trans fail safe error message but we were told that had nothing to do with it. Is it possible that when the alternator died that it fried the nav system?

Sure - a dying alternator, which is actually the voltage regulator, not the windings, could send a pulse through the system just like an incorrectly disconnected battery.

Should have been pretty obvious though - if the Nav worked when you ttok it in then the issue was the battery being disconnected. If it didn't, then the issue was the alternator.

d-