An NTLDR missing message when a user starts up a computer means a major problem exists in an important section of the hard disk responsible for continuing the boot sequence.
In the Windows operating systems that preceded Vista, the start of a boot up sequence included loading a small program called NTLDR, which pulls up the initial start menu.
The NTLDR program is located on the hard disk or on a bootable floppy in the section called the “boot sector.”
Windows computers need this start menu process in order let the user choose different operating systems to load or just to continue booting up the computer.
NTLDR, like any file, can become corrupted and appear to be missing. Trying to boot from a non-bootable floppy will cause the error, as will incorrect installations of different operating systems.
Microsoft recommends either using a good book disk to get the computer working, using the Recovery Console, or the installation CD for operating system.