Problem re-installing windows xp

Best thing you can do is format the drive and re-install from scratch, if you have data that you'd like to keep, look for windows xp bootable (free) and boot from that disc, copy whatever you need to a USB (make sure the files are clean!).

Then you just need to buy a copy of windows and install it since you don't seem to have installation media nor CD KEY

I do have the CD-Key, is there a way I can you the copy of windows I have.

what you're trying to do is simple but your problem is your xp cd is not bootable.  first thing first.  how old is the pc and does it have a floppy drive.  also i'm assuming that the pc is new enough where it will boot from a cd?  you need to setup a bootable cd or floppy that mounts the cd drive and assigns a drive letter to it.  once this is done, boot to the bootable disk and the insert the xp cd in the drive, in your command prompt you need to navigate to the cd drive letter, change directory to /i386 and execute the winnt.exe which will start the xp setup program.  i like to delete the existing partition, create a new one, and do a quick format on it to get rid of any trace of the old os, then follow the rest of the installation process.

let me know the answers to the questions at the beginning and also if you need help creating a bootable cd or floppy.

Depends a lot on your current installation.
Does this scenario apply to you system?
http://www.howtohaven.com/system/createwindowssetupdisk.shtml

I do have a floppy drive, however it is a USB floppy drive, The system will boot from the CD drive.
The computer is an HP Compaq dc5800 small with an s-ata hard drive

Detailed step by step instructions will be great.

Detailed step by step directions are at the link MASQUERAID posted already.  Here it is again.

How to Create a Bootable Windows XP Setup CD/DVD on a System with Windows Pre-loaded

>>  The computer got a virus and now wont reboot  <<   what happens?  any messages or errors?

Thanks for the help, I got it working using boot files to load the CD and Hard Drive, then loaded the OS from the CD.