Long answer here but this is what i print out for customers.
NTLDR is Missing Error Resolution
From Tim Fisher,
Steps to Resolve the NTLDR is Missing Error in Windows XP
NTLDR Error Message
There are few different ways that the "NTLDR is missing" error may present itself, with the first listing being the most common:
* "NTLDR is missing
Press any key to restart"
* "NTLDR is missing
Press Ctrl Alt Del to restart"
* "Boot: Couldn't find NTLDR
Please insert another disk"
The "NTLDR is missing" error displays very shortly after the computer is first started, immediately after the Power On Self Test (POST) is complete. Windows XP has only initially begun to load when the NTLDR error message appears.
Causes of NTLDR Errors
There are a number of possible causes for NTLDR errors, including the most common "NTLDR is missing" error message.
The most common reason for this error is when your PC is trying to boot from a hard drive or flash drive that is not properly configured to be booted from; in other words, it's trying to boot from a non-bootable source. This also would apply to media on an optical drive or floppy drive that you're trying to boot from.
Other possible causes include corrupt and misconfigured files, hard drive and operating system upgrade issues, corrupt hard drive sectors, an outdated BIOS, and damaged or loose IDE cables.
Fixes for NTLDR Errors
1. Restart the PC. The NTLDR error could be a fluke.
2. Check your floppy and optical (CD/DVD) drives for media. Often times, the "NTLDR is Missing" error will appear if your PC is trying to boot to a non-bootable floppy disk or CD/DVD.http://pcsupport.abo...orderchange.htm
Note: If you find that this is the cause of your problem and it's happening a lot, you might want to consider changing the boot order in BIOS so the hard drive is listed first.
3. Check the hard drive and other drive settings in BIOS and ensure they are correct. The BIOS configuration tells the computer how to use a drive so incorrect settings can cause problems, including NTLDR errors. There is usually an Auto setting for hard drive and optical drive configurations in BIOS which is usually a safe bet if you're not sure what to do.
4. Restore the NTLDR and ntdetect.com files from the Windows XP CD. Restoring these two important system files from the original Windows XP CD may do the trick.http://pcsupport.abo...ldrntdetect.htm
5. Repair or replace the boot.ini file. This will prevent the NTLDR error if the cause of the problem is a boot.ini file that is not configured properly for your Windows XP installation.http://pcsupport.abo...pairbootini.htm
6. Write a new partition boot sector to the Windows XP system partition. If the partition boot sector has become corrupt or isn't properly configured, you may receive the "NTLDR is Missing" error.http://pcsupport.abo...wbootsector.htm
7. Repair the Windows XP master boot record. NTLDR error messages may also appear if the master boot record is corrupt.http://pcsupport.abo...t/repairmbr.htm
8. Open your computer's case and ensure that the cable that connects the hard drive to the motherboard is firmly in place. If this does not resolve the issue, try replacing the cable. NTLDR error messages could be caused by loose or malfunctioning IDE cables.
9. Update your motherboard's BIOS. Occasionally, an outdated BIOS version can cause the "NTLDR is Missing" error.
10. Perform a repair installation of Windows XP. This type of installation should replace any missing or corrupt files. Continue troubleshooting if this does not resolve the issue.http://pcsupport.abo...stxprepair1.htm
11. Perform a clean installation of Windows XP. This type of installation will completely remove Windows XP from your PC and install it again from scratch. While this will almost certainly resolve any NTLDR errors, it is a time consuming process due to the fact that all of your data must be backed up and then later restored.http://pcsupport.abo...nstxpclean1.htm
If you can't gain access to your files to back them up, understand that you will lose them all if you continue with a clean installation of Windows XP.
12. Finally, if all else has failed, including the clean installation from the last step, you're most likely facing a hardware issue with your hard drive. Replace the hard drive and then perform a new installation of Windows XP.
NTLDR Errors Apply To
This issue applies to the Windows XP operating system, including Windows XP Professional and Windows XP Home Edition. Windows Vista does not utilize NTLDR.