2001 740il audio problems

One cold morning my wife started my car for me & when i went out the Nav screen was black & the radio was off. Now when i turn the car on the radio plays for about 3 minutes then cuts off. If i power the radio off/on it will play for another 3 minutes everytime i do this & then cut off again. Don't know where to start. Radio? Head unit? Nav? Screen? Please help

the nav comp is bad.

have same problem on 01 740i which happened AFTER AAA youth tried to jump start incorrectly. Diagnosis is bad NAV. Dealer pricing for same is pricey
But even after market or from elsewhere is going to run $900 on up
The radio goes off because its function is connected to the NAV computer...after it scans around briefly it apparently detects a prob and shuts down. Radio itself is likely ok

We are now looking for a replacement that is updated...eg with bluetooth for the fone, NAV of course, and radio that all will hook into existing amplifier and speakers AND also integrate witht he dashboard panel messaging. Am told they exist but am just beginning the search

sounds like the nav unit in the trunk. quite a common problem. mine was out when i bought the car due to improper battery charging. dealer fixed it with a new unit, quite expensive. but well worth it. they paid for it though.