Mine did this about 6 or 7 years ago, it would come back on after restart usually, I replaced the battery shortly after for another reason and it has rarely done it since.
You may need your firmware to be upgraded. I had a problem whereby I could switch on the radio however the display and blue tooth would cut out and not work unless I rebooted it. A dealer upgrade of the firmware solved the issue. Mine was a 2011 db9
