CD/DVD not showing up in 'my computer'

And all of a sudden I lost my CD/DVD in 'my computer'

The device shows up when starting my pc up and in the BIOS/CMOS but does NOT show up in device manager nor in Computer Management.

There are no filters to be deleted in the relevant registry entry.

Under the dos -prompt, in the volume list, the device doesn't show when there is a cd in the drive.

I replaced the actual piece of equipment (3 times), the power pack and all the cables, but still no change.

Have I inadvertently 'disabled' something in the BIOS/CMOS set up I shouldn't have ?

Running XP Pro SP3

An urgent reply would be appreciated (preferably in plain english as I'm not a pc geek)