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How to Replace an Invalid Security ID With Default Security ID

Windows stores files on hard drives using the NTFS. The NTFS supports permissions, which specify which users can access which files and whether they can write to them or not. Each file on an NTFS has a security ID, which points to a location on the file system where NTFS stores the file's security information. If the NTFS becomes corrupted because of software or hardware errors, some files could have security IDs that don't point to a valid location. The chkdsk program scans for such files and replaces their invalid security IDs with the default security ID, in addition to fixing other file system errors.

1). Click "Start," "All Programs" and "Accessories."

2). Right-click "Command Prompt" and click "Run as Administrator."

3). Type "Chkdsk C: /f" into the command prompt window and press "Enter." If you want to scan a different drive for errors, type its drive letter instead of "C:."

4). Type "Y" and press "Enter" if you're asked whether you want to schedule a file system check for the next time the system boots.

5). Restart your computer by clicking "Start," clicking the arrow to the right of "Shut Down" and clicking "Restart." Windows automatically finds any invalid security IDs on the file system and replaces them with the default security ID after it restarts.