How to repair a missing or corrupted system file in Windows

1. Open an elevated command prompt. To do this, do the following as your appropriate:
    

   Windows 8.1 or Windows 8

   Swipe in from the right edge of the screen, and then tap Search. Or, if you are using a mouse, point to the lower-right corner of the screen, and then click Search. Type Command Prompt in the Search box, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.

   

    

   Windows 10, Windows 7, or Windows Vista

    

   To do this, click Start, type Command Prompt or cmd in the Search box, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.
   

   

    

2. If you are running Windows 10, Windows 8.1 or Windows 8, first run the inbox Deployment Image Servicing and Management (DISM) tool prior to running the System File Checker.  (If you are running Windows 7 or Windows Vista, skip to Step 3.) 

Type the following command, and then press Enter.  It may take several minutes for the command operation to be completed.

3. At the command prompt, type the following command, and then press ENTER:

 
 The sfc /scannow command will scan all protected system files, and replace corrupted files with a cached copy that is located in a compressed folder at %WinDir%\System32\dllcache.
The %WinDir% placeholder represents the Windows operating system folder. For example, C:\Windows.

Note: Do not close this Command Prompt window until the verification is 100% complete. The scan results will be shown after this process is finished.