That could be caused by a general electrical issue like a bad battery or bad ignition switch.

Is your battery original, or is the hydrometer/sight glass a green dot or a black dot. If you have the black dot, then you may need a new battey. Here is a test you could attempt. Connect the car to a battery charger and then try to operate the radio. If the behavior changes, then it is your battery.

The other possible problem is the ignition switch. This can cause similar symptoms on the E53, E38, and E39. I assume that the E46 would have the same vulnerability and symptomatic behavior.

If it is not power, then you could just have a dead nav computer.

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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