Restoring back to new

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Can any one please tell me how to restore my windows xp back to original
condition when first bought. I bought my cmputer second hand and whn I got
it, it was if it was new and logging on for the first time. I have tried to
restore it back but I can only go back to Jan 08. (Restore point) I have up
loaded all files etc to an external hard drive. I also log into the computer
as the administration user. I want to basicly wipe everything and start
again. Can you please help. Thanks
.