5D mkII no audio recording internal mic
There is a little switch in the connector for the external mic. Try to plug it in, and unplug it several times. The switch might have stuck, so it "thinks" that an external mic is connected. My 60D did that twice.
Or you have to let it go back so they can reconnect the mic at the servicecenter - they may have screwed up when they put it together last time .
Henrik N. J.