How to solve NTLDR is missing in windows XP issue
Using Windows recovery console. The Windows 2000 and Windows XP CDs supplied by Microsoft has a tool called the Recovery Console which can be used to repair errors that prevent Windows XP from starting using the command line. OEM versions of Windows XP, including computers that were supplied with Windows XP preinstalled, may not have this utility. This problem may occur if the basic input/output system (BIOS) on your computer is outdated, or if one or more of the following Windows boot files are missing or damaged: Ntldr
Ntdetect.com
Boot.ini Check your drives for floppy,USB storage devices,CDs and any other bootable media.Because sometmes these things makes problems.Then go to BIOS and do the BIOS settings to boot from the source where the OS is installed. 1: Insert the Windows XP bootable CD into the computer. 2: When prompted to press any key to boot from the CD, press any key.
3: Once in the Windows XP setup menu press the "R" key to repair Windows.
4: Log into your Windows installation by pressing the "1" key(most of the cases it will be "1" only) and pressing enter.
5: You will then be prompted for your administrator password, enter that password. 6: From the command prompt, copy NTLDR and NTDETECT.COM from the i386 folder of the CD to the root folder of the hard drive. In the example commands given below, C: is the hard drive and D: is the CD-ROM drive. You will need to change the drive letters if appropriate:
COPY D:I386NTLDR C:
COPY D:I386NTDETECT.COM C:
Once both of these files have been successfully copied, remove the CD from the computer and reboot.

Ref: http://www.soluzia.net/ntldr-is-missing.php