My cdrom is not listed in device manager or also not shown in my computer programm.. no icon of cd rom in my computer

What version of Windows? Have you tried rebooting? Have you recently opened the case? Is it a CD/ROM or a burner?

What version of Windows? Have you tried rebooting? Have you recently opened the case? Is it a CD/ROM or a burner?
I am using windows Xp after opening the case it was not working

First, when asked for more info, please provide ALL info requested. It may be necessary to diagnose the problem.

If you opened the case and it stopped working you probably loosened some cables. Go back in and make sure all cables are seated properly.