Okie,
this is my suggestion:
FIRST reformat. Do a full format and not a quick one. Use a windows98 bootdisk, format C:/ drive... Once you have formatted then, do the following:

Get into your BIOS, set everything to default, exit and save changes.
Then go back into your BIOS, change Plug N Play OS to NO, then change the boot drive order to CDROM first, then HDD, then Floppy drive.

Now exit saving changes. NOw power off the PC, but your windows XP CD in the drive. Then power on, you should now see the press any key to boot from this CD. If it won't let you boot to the CD after that, then you need to get an alternate source to XP, how you do that is up to you.
Then retry. If it still does not work, perhaps you need to update the BIOS on your motherboard. Just go to the manufacturers website, and look for the most recent update to your BIOS. MAKE SURE YOU HAVE THE CORRECT BIOS

If none of that helps, repost and I will see what else I can come up with,
BB