Have you also changed the IDE cable just in case it's defective?
And is the jumper set correctly?
Was there any message about corrupt registry?
Did you try system restore back to before this happened?
Review these links on similar issue:
http://www.google.ca/search?hl=en&ie=UTF-8&oe=UTF-8&q=cd-rom+disappeared+xp&btnG=Google+Search&meta=
All of a sudden my cd-rom stopped working. I even changed out the unit. Still doesn't work. Doesn't even show up when I click My Computer. When I go into Help & Support System Info, it shows cd-rom as "not installed". What happenned??

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