Been having a couple of problems on the e53 with the radio. Was a few times where the radio would not shut off, even after turning off the car. It would eventually turn off, I don't remember exactly how long it took or what I did, if anything, to get it to turn off.
Now, I shut the car off, while the radio was on, then came back 5 minutes later, started the car, and no radio. Pushing the 'On" button does nothing. All nav, board monitor and other functions work as normally.
I have pulled all the fuses related to the radio, turned the ignition on with the fuses out, replaced the fuses, still nothing. Have also unhooked/rehooked the battery.

Any other ideas?