This particular problem has been showing up time and again, and just about every registry "fixer" tool has missed this solution, so kudos to the folks at www.pchell.com for documenting it. This is now the fourth machine that I've run into that the optical drives have mysteriously disappeared. The symptom is that the device manager in both XP and Vista has indicated that the device cannot be found and shows up with the annoying yellow exclamation point in the device list. The owners of the other three machines finally gave up and just restored or gave up and regenned the machine. By the time it hit my Vista video laptop, my curiosity bone refused to give up, especially when an external USB optical DVD drive got detected just fine, but also showed up with the yellow exclamation point.
Using the Vista "System Information" tool, I browsed to the section on the CD/DVD drive and found error code 39. So why didn't the hardware manager tell me this?! What I found was that the PC Hell site had just the solution and that was some leftover junk from a previous piece of software that touched the CD/DVD portion of the registry. Simply by deleting two registry key entries, I was able to reboot and revive the optical drive.