NTLDR (NT Loader) is the most essential file that is needed by the Windows NT (Server 2003, XP, and Server 2000) systems to boot. It is run from the primary hard disk drive and contains the main Boot loader. The well-being of NTLDR is very significant for the boot process as if this file is missing, then your system would not be able to boot.
The NTLDR file may get missing or corrupted due to various reasons, such as virus infections, power outages, damaged operating system, etc. In such cases, you should consider taking appropriate corrective measures to rectify the problem.