|go to your BIOS seup utility and set USB legacy support to enabled.|
to restore your missing NTLDR, boot from your XP installaton CD into the Recovery Console, at the command prompt type the following two commands, pressing Enter after each one:
copy d:\i386\ntldr c:\
copy d:\i386\ntdetect.com c:\
(In the command listed above, d: represents the drive letter assigned to the optical drive that your Windows XP CD is currently in. While this is most often d, your system could assign a different letter. Also, c:\ represents the root folder of the partition that Windows XP is currently installed on. Again, this is most often the case but your system could be different.)
If you're prompted to overwrite either of the two files, press Y.
Take out the Windows XP CD, type exit and then press Enter to restart your PC.
Assuming that missing or corrupt versions of the NTLDR and/or Ntdetect.com files were your only issues, Windows XP should now start normally.