You presumably mean an XP Repair and this has to (normally) be done from a "proper" XP installation disk.
If you go into the Bios (on bootup press Del or whatever is needed to enter Setup).
When the Bios screen comes up you need to configure to boot from CD rather than a floppy (A) or whatever is listed.
Save and Exit with your XP disk in your drive and follow the instructions.
A good guide can be found at:
Make sure that you keep pressing Install until you have the option to do a Repair (NOT Recovery Console); you will/may also need your product key handy.