There are many people to install the original Windows XP system in the use of USB flash disk,but reboot the system after installation, sometimes prompted the error message NTLDR is missing press any key to restart.Then it has stoped there, can not enter the system.What is wrong with it ?The cause is system root file is missing or damaged. Obviously the system has been installed, but can not enter,actually is that the crucial step in the installation was wrong. Here let's to see the right way to install Windows XP by USB flash disk.

The first step,set the Windows XP system image on the local disk (not system partition, such as the E:)

The second step, insert the USB flash disk.,open Ultraiso, open the WinPE image, click "start" -> "write disk image".

The third step, select the USB flash disk, click Start (better you should format the USB flash disk first )

The fourth step,after the burning is complete, click Close and restart the computer (set the boot sequence USB-HDD mode first)

The fifth step,enter the WinPE system. When WinPE boot is completed, insure to unplug the USB flash disk,otherwise you directly install, it would prompt NTLDR is missing(this is a crucial step .)

......

This  more visit http://www.computerites.com/computer-skills/2011/12/causes-and-solutions-of-ntldr-is-missing-error-when-installing-windows-xp-system-by-usb-flash-disk-199.html