With a 07 750il dont expect to get any help from internet forums. The 7's are so technical that BMW technicans take a 2 week training class on them.
With your radio not working is might be a programming issue with your "CCC" moduel which controls all your entertainment devices.
The message you might possibly be reciving for your key is that the battery in the key remote is discharged and needs to be charged.
Thats why the car will not start with the key in your pocket, the key is not sending a signal to the vehicle to start, it needs a direct input from your ignition.
If you do not charge your key once in a while your lock/unlock and comfort access start will not work, as in your case. Only way to charge the key is to put it into the slot while you drive.