GARDENER,
In your BIOS set the CD Drive to boot before the Hard Drive. Put your WinXP CD in the CD Drive and turn the computer on. When the it says "Press enter to boot from CD", do so. You do not want to use Recovery Console. (When that option comes up, it ENTER to keep WinXP installing.) Then the CD will look for previous installations of WinXP. When it finds it, you will have to option to it "R" to do a Repair. (Do not get confused with Recovery Console which also tells you to hit "R" in the previous screen to the one you want.)
Then you hit F8 when you access to the M$ Licence, after that you enter your CD-Key, and the Repair will go from there.
Take Care,
Richard