What happened? (How NTLDR works and why your PC can't find it)
When your computer starts, the BIOS attempts to find the primary hard drive's active partition to read the first sector for the MBR (Master Boot Record), it uses that info to load the rest of the OS. For Windows NT4/2k/XP the MBR is pointed to the NTLDR (New Technology Loader) and it takes it from there. If you get the "NTLDR is missing, press any key to restart" what's most likely going on is the BIOS either didn't look for the right drive, didn't find the right partition, it wasn't active, didn't find the MBR, or the MBR didn't list NTLDR in the right place, the location of NTLDR changed, or you are looking at a hardware failure situation (memory/cables/drive/motherboard/etc).
The first thing to do is try to change back whatever hardware or software change you just made (this could be as simple as leaving a floppy disk in the drive or you need to reseat the cables). If the contents of the drive are especially important and you have no backups, I would recommend removing the hard drive, placing in an enclosure, and backing up the data first, in fact, backup all of your computers. (What if I made new changes that I want to keep?).
Make a NTLDR boot disk to get back into Windows.
The quick test to make sure your OS installation is still good is to create an MBR and NTLDR on a floppy disk and check if you can just boot back up into your system, this disk will check many of the partitions for a working windows installation. Here are the instructions to do this:
1. Get a blank floppy/cd-r/usb (whatever is on it will be erased), and put it into a working computer.
2. If you have a working Windows machine download my fix: Floppy fixntldr.exe | CD-R fixntldriso.zip | USB ntldrusb.zip onto a working computer (Backup copies of these files available at http://ntldrismissing.com )
(What if I don't want to download a file from a website I don't trust?). (64 bit WinXP Floppy 64ntflop.exe | CD-R 64ntiso.zip | Files 64ntfile.zip)
Do you remember if the broken computers had the Windows installation in "Windows"? If you can't remember just keep going (What if it was not named Windows but WINNT like in NT4 or 2000?) .
(If your backup system is NT4 or Windows 2000: What if my backup system is Mac / Linux or another alt OS?).
3. Make the new boot disk:
*Floppy: Run the fixntldr.exe file by double clicking it. Click OK to overwrite the blank floppy disc in the working computer, you should see some screens about writing a new floppy disk. (If you don't like running an exe from me, you can run fixntldr_RawRite.zip and just replace the RawRite.exe file inside with one you trust) (now go to step 4)
*CD-R: This is not a normal file you burn to a CD, it is an "ISO" file, you must first extract the fixntldriso.zip file by right clicking it and choosing "Extract All" then Next>Next>Finish then download a program called "ISO Recorder" from here http://isorecorder.alexfeinman.com/isorecorder.htm (Windows 2000 users use Active ISO Burner IsoBurner-Setup.exe) and install it. Once it's installed, right click the fixntldr.iso file and choose to "Copy image to CD" or "Burn ISO file" and let it burn the cd (now go to step 4)
*USB: Right click the ntldrusb.zip file and choose "Extract All" Next>Next>Finish
Then Insert your USB Stick into the working computer (remove any other USB sticks, and be sure there isn't anything on the USB stick that you want since we are about to erase it);
Double-click HPUSBFW.EXE in the ntldrusb folder;
Check "Create a DOS startup disk" and "using DOS system files located at" then press the grey button with the "...";
A box will come up asking you which folder to select, point it to the "dos system files" folder;
Press OK; Press Start; Press Yes; Let it run for just a few minutes till a new box comes up; Press OK; Press Close;
Open the "putonusb" folder, copy all the files, paste them onto the usb stick (just in the root of the drive, like E:\);
Eject the USB Stick; Remove it from your computer;
Place it into the computer with the "NTLDR is missing" issue, reboot it.
You will see the Windows 98 screen pop up for a second, then you will see a black screen with white letters prompting you to "replace boot sector of the drive C: (y/n)", press the y key;
It will go to a C:\ prompt, reboot the computer by pressing Ctrl+Alt+Del; (now go to step 4)
4. Put the new floppy/cd-r/usb you have just created into the computer that gets the NTLDR is missing error message, turn the broken computer off.
Using the boot disk in the computer with the "NTLDR is missing" error.
Start back up the broken computer with the floppy/cd-r/usb inside it/plugged into it. Once your computer gets past the BIOS screen your computer should try to access the boot disk and you should see a black screen with white letters (What if I don't see this screen?). that says:
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