My windows xp was not genuine I am activated now but wish to register I do have product key can I do this without a new install
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If you initially installed a copy of XP that was not a genuine copy, then I would recommend you install the genuine copy.
There is no way of knowing how the original version might interact with other software. After installing the genuine version, then you can use your key to register it. While there may be ways of registering the copy that is not genuine, I suspect you could be just asking for problems.