I had this problem as well. All had been going fine on my XP Pro machine for over a year and then all of the sudden, the disk drives were gone. They couldn't be found in Windows Explorer, didn't appear in the folder list, and had little exclamation points in yellow circles on the Device Manager with warnings that the drivers loaded but Windows couldn't find the drives. I went to setup in BIOS and, sure enough, BIOS detected them and knew that they were there, but XP just couldn't find them. I tried everything from rebooting the machine to deleting the IDE channel and beyond, but to no avail. Then I found the following at http://www.careyholzman.com/WinXP.htm:
Problem: My DVD-ROM drive disappeared! Also, the little red light on the drive is permanently on and the drawer won't open.
Possible Solution: This is a well known problem with XP, if you cannot access CDROM, DVD, CDR or CDRW drives or get a Code 31 or 39 error in Device Manager then the solution is to run Regedit and delete Upperfilters and LowerFilters at:
And then restart the PC
I tried it and it worked like a charm. My drives reappeared.