Use this repair option. Your data will still be there.
Press any key to boot to CDROM, and the XP setup should start.
When prompted, press enter to install XP. It will find your previous install and then you select “Repair”. After that do not press any key to boot to CDROM no matter how many times the XP setup reboots the system.
If that doesn’t work, then it’s time for a clean install. For that, follow the above steps, but don’t use the repair option. Continue on and delete the C:windows partition and then create a new one. It will then format and install XP.
Good luck!