NTFS (NT file system) is the standard file system used by Microsoft Windows operating systems since the release of Microsoft Windows NT. NTFS is an improvement over the prior FAT file system, offering improved reliability and security, but it's also prone to developing NTFS errors, which can cause your system to become unbootable. When you encounter an NTFS error, you can attempt to repair the disk and continue with your work, but it will take a bit of troubleshooting to do so.
First try to run the disk repair utility by using an alternate boot-up process. Turn your computer on and tap "F8" while it's booting (or whichever key is listed on your screen during start up). This will take you to a boot menu with boot options presented. Choose "Safe Mode" and continue booting. This mode is a stripped-down version of Windows without most drivers loaded.
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Go to "My Computer" from the "Start" menu and highlight the drive on which you're experiencing the NTFS errors. Right-click on the affected drive and choose the "Properties" option. This will open the drive properties window. Select the "Tools" tab and select the option to "check the drive for errors." The system will then run through the drive check utility, repairing the NTFS error present.
If that isn't successful, access the repair console by placing your Windows System Installation disk into the drive. Turn your computer off, and then turn it on again to load the disk. Choose "boot from disk in CD-ROM drive" during your computer's boot-up sequence (tap F8 as you did before to enter setup and change the boot option). Choose to enter the repair console when offered the choice on screen. The repair console will appear as a text prompt, for example "A:>." Enter "chkdsk a:" with the actual drive letter of your troubled drive replacing the "a:"--chkdsk will run on your system and repair the NTFS error on the affected drive.
Move the drive to a second PC if the affected disk is your boot hard drive and you cannot access safe mode and your system installation disc is unavailable. Connect the hard drive to the second PC and use the safe mode on the unaffected PC's operating system to repair the drive.