Problem w/ Missing Optical Drive- Did regedit tweak, might’ve screwed it up

I’m running XP Pro and all of a sudden my optical drive isn’t showing up. Someone told me to clear the values for the Upper and Lower filters, then reboot. Well, I did just that and there has been no change, other than in the registry, which worries me that I may have been told wrong…?
I could really use some help figuring this out, it’s been driving me crazy the past few days. Does anyone know how to fix it?