[ubuntu] cant unmount cd drive

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http://ubuntuforums.org – when i put a dvd or cd in my cd drive i used to get a box asking what to do. ive noe set it to do nothing and not show that box again.. now when i want to burn a disc it says no burner ready, disc may be in use, please unmount drive. i cant see any way to unmount the drive please help (Hardware)