Understand the causes of missing NTLDR errors. One of the most common reasons for an NTLDR-based startup error occurs when Windows XP attempts to start from a hard drive that isn’t set up to launch Windows XP. For example, you may encounter an NTLDR error if you attempt to boot from an improperly formatted Windows XP startup disk. These errors may also be caused by corrupt, missing hard drive data and loose hardware cables. And sometimes caused from abrapt shutdown without proper procedure, removal of hardwares withough shutting down the system or disabling them. etc.