Desktop disappears when cd is inserted in drive

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http://www.ubuntux.org – Hi, i have been using ubuntu 9.04 since june09. But i have an issue. Whenever I insert any cd in cd drive, the desktop disappears while the taskbar is there. No icons on desktop. It seems ubuntu is trying to read cd or whatever, but desktop icons disappear! Then i press Crtl+alt+backspace with cd still inside, but login window appears. after i login, it is still the same- no desktop. those cds work well on windows XP. What could be the issue. I will post any details required about system. In fact, I have linux mint7 installed with ubuntu 9.04 alongside XP on this system. Same issues with mint7. CAn anyone help! (Distributions)