To reinstall, not a full reinstall, just a repair reinstall
Type Exit
Reboot
At the welcome screen, choose enter.
Once at the license agreement, press F8.
At the next screen, choose to repair the selected Windows XP installation by pressing R.
The files will begin to install and then your PC will reboot. During the reboot you will be presented with option of booting from the CD again by pressing any key. Don't press anything. Allow it to finish the install without booting from the CD again.