This happens quite often if one of the third-party packages has been uninstalled. They add references in the Registry for modules which they use, and these references fail to be removed, leaving Windows unable to find the files apparently needed for CD devices at the next boot. There is a simple Registry patch to correct this (download it here). Before using the patch, be sure to back up the Registry. After using the patch and rebooting, the drives should reappear. Any third party package that is still required will then need to be re-installed.

This problem also may arise if there is underlying trouble with the Input-Output system of the machine: for example, interactions with controllers like Promise or Highpoint, or with special drivers. It may be worth trying a change in the DMA settings for the device in Control Panel | System | Hardware | Device Manager. Under IDE controllers, double click on the Primary or Secondary IDE Channel concerned, then click the tab for the Advanced Settings page.

Source: http://aumha.org/win5/a/xpcd.php

--
Moderation: added source

This post has been edited by fariz: May 3 2006, 02:15 PM