My Dell did not come with disks and I recently had to reinstall XP Pro on it. I did have a disk from another computer that I scrapped for parts so I used it. When I tried to enter the product key from the dell it said it wasn't valid so I used the product key from the disk and finished the installation. Now it is saying I can't install SP3 and other programs because of code. Microsoft also acts like it is not even XP PRO. How can I fix this w/o buying another Windows installation disk?