Help: CDROM Drives Disappear in XP-Pro

OK i'm running a machine i built. P4 with an Asus Mboard.
it's about a year old. the BIOS is updated and the CDrom
drive ARE recognized in the BIOS, but some how they
disappear in My Computer. I ran the usual stuff: Hardware
Wizard (under Advanced mode), and Device Manager. I guess
all this actually started after i Defrag-ed the drive
(60GB IBM Hdd). I have gone into the option of my "Last
Good Configuration" and that worked for a while, then it
started up again. The last thing I'm thinking of is re-
installing Win XP Pro, overwriting everything. I'm just
running out of options. Suggestions would be great.