As Ken has said make sure that no CD's or Diskettes are in these drives
when the computer boots. If no disks are in these drives then try
booting the computer with a boot diskette, or with your Windows XP CD if
your computer has no diskette drive. To make a boot diskette see here:
http://www.nu2.nu/bootdisk/ntboot/
If your pc has no diskette drive (or if you wish) you can boot with the
Windows XP CD and start the Recovery Console. Once in the Recovery
Console try to boot to the Windows installation with the logon command.
Description of the Windows XP Recovery Console
http://support.microsoft.com/default.aspx?scid=kb;EN-US;314058
If you chose to boot with a diskette or with the Windows XP CD, you may
have to go in the BIOS and change the boot device order so that the
diskette or CD is set before the hard drive in the boot order.
Let us know if the computer can be booted using one of these methods.
John