Hello and thank you for using this service,
I think your question may have been cut off. Please tell me in detail the error message, and where/when you are getting it.
Which Windows? XP, Vista, 7, or 8?
Do you have an XP installation CD? You will need this for us to proceed.
With this type of problem , you'll need a working CD drive to boot from on the computer, or you'll have to physically remove the hard drive and mount to another computer (preferably also running Windows XP). I'm assuming this is a desktop (not laptop) computer.