This just happened to me. I don't know if it's related to a recent series of Microsoft Windows updates I applied or not.
1. I verified that the drives were being seen by the Bios, so it wasn't a hardware issue.
2. Devices Manager had exclamation points on the drive entries and said that the hardware could not be detected.
3. I removed the CD-ROM drive devices and rebooted.
4. Windows detected them reinstalled them again, but they still did not appear in Explorer.
5. This time Device Manager gave me "I get this error message Windows cannot start this hardware device because its configuration information (in the registry) is incomplete or damaged. (Code 19)" as an explanation for the exclamations.
6. After some quick Googling, I came up with the solution of deleting the UpperFilters and LowerFilters registry keys from "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E965-E325-11CE-BFC1-08002BE10318}" (I only had a LowerFilters key) and rebooting.
Everything was fine after that.
CD-ROM drives missing from Explorer.
Moderator: jasonb