US Spec 2002 X5 3.0 with factory installed CD based 4:3 screen NAV system.

Ever since the battery was replaced, the nav screen has been blank. Radio still works. The LED on the NAV unit in the back of the car still lights with the ignition (on the eject button). After turning off ignition, it remains lit solid for about 30-60 sec and then turns off without blinking. It does reappear if a door is opened.

I need to figure out if the NAV computer is bad (as many posts here suggest) and test it to definitively diagnose. Or could it possibly be a bad screen?

I would consider getting the DVD based MK4 unit if this is bad--any referral to a good place to buy would be helpful also.

Thanks for the info.