Ray, I've encountered this problem in the past and found the answer but can't remember what I did to solve it now. I have a CD-ROM and a DVD drive but, all at once, Windows doesn't see them anymore in "My Computer" and "Explorer". When I boot Windows, they are shown in the start-up window and, if I check Device manager, it says that they are working properly. I think that this happened after I switched from XP Pro to XP PRO 64 bit because they HAD to be working for the install. And, if the drives need XP PRO 64 bit drivers, I would think that Device Manager would tell me so. Any ideas???   

No.  Maybe someone else has some ideas.

In several Microsoft kb articles, two registry entries keep showing up for causing missing drives. Apparently these can become corrupted and cause this problem.
This is one concerning CD and DVD drives.
http://support.microsoft.com/kb/314060/

Thanks for the help guys. You have done it again. I tried the Microsoft "Registry Edit" and, after rebooting, my CD & DVD drives are now both listed in Windows Explorer & Device Manager. I'm saving a copy of the fix to my files just in case it happens again. Happy As A Clam!!!