Repair Windows With System File Checker

How to use System File Checker (SFC) – a utility in Windows to scan for and restore missing/corrupted files. SFC can help repair Windows if it is not working properly because important system files have been modified – by viruses, hard drive corruption or badly written software.

System File Checker looks for any changes to important system files – if changes are found, the modified file is restored to a genuine clean version from a saved copy located in the Windows\System32\dllcache folder.

If the file is not in the dllcache folder (or the dllcache folder is also corrupted), you will be prompted to insert your Windows installation disc – a genuine clean version of the file will be restored from there. There are several prerequisites for SFC to work:

  • System File Checker can only be run from Windows – in normal mode or safe mode. It can’t run from the Recovery Console so it is of no use if you are unable to log in.
  • If the dllcache folder does not have a saved copy of the corrupted file (in our experience it rarely does!) you must have a full Windows installation disk available – a manufacturer’s ‘factory restore’ disk or a restore disk you had to burn yourself is not enough.

Unfortunately modern computers often don’t come with a full Windows installation disk. However, if you have Windows 7 you can freely download a legal copy and burn it to a DVD – see our article Free Download of Windows 7 Including SP1.

  • The other ‘gotcha’ is that the installation disk must include the same Service Pack (SP) as that installed on your computer. E.g. if you have XP SP3 on your computer you must use an XP SP3 CD – an original XP SP2 CD will not work as the files on it are far older than the files on your computer.

Likewise, if you have W7 SP1 on your computer (which you should as SP1 was released earlier this year) you can’t use an original W7 disk – you need a full W7 disc that includes SP1. All the more reason to download the full W7 SP1 disk as otherwise you will never be able to run SFC in future!

How To Run SFC – the method differs slightly depending on the version of Windows:

XP – Click ‘Start’ then click ‘Run’ and type in SFC.EXE /SCANNOW (note the single space between sfc.exe and /scannow). Press the Enter key to start SFC – it could take up to an hour. Skip to the ‘All Windows’ section below.

Vista/Windows 7 – Click ‘Start’ and type command in the search box. At the top of the search results, right click on Command Prompt and select ‘Run As Administrator‘ (click Yes if the User Account Control message appears) to open an elevated (admin level) command prompt window. In the command prompt window, type in SFC.EXE /SCANNOW (note the single space between sfc.exe and /scannow). Press the Enter key to start SFC – it could take up to an hour.

All Windows – If the program asks for your Windows Installation disk, insert your full CD/DVD (with the correct SP included). When the SFC program has finished it closes itself but does not confirm anything to you.

After SFC Finishes

  • If it did not ask you to insert your installation disk this means that it wasn’t necessary to replace any files – you will need to look at other solutions to repair Windows.
  • If it did ask you to insert your installation disc this means that it has replaced corrupted/missing system files with genuine clean ones – restart your computer for them to take effect and hopefully they will have cured your problem.

Tip: when your computer has restarted you must visit Windows Update and check for new updates to your computer. This is important because SFC may have replaced some of your files (that were previously updated) with older versions from your installation disk. To check this (and to update any of those files if required) you must allow Windows Update to check your computer for updates and update it if needed.

6 Responses to: "Repair Windows With System File Checker"

  1. david says:

    thnaks for the tip on the 7 download! My laptop never came with a disc but I’m downloading it now

  2. Bernice says:

    Ok so my original installation was XP sp2, but now it has sp3 installed and i’m using sfc /scannow and it is asking for the installation cd (which isn’t sp3) what do i do now?

    • Roy says:

      You’d have to find/beg/borrow an XP SP3 CD from someone.

      Or if you have access to another PC you could try to burn a new one by slipstreaming SP3 into your SP2 CD – not for the fainthearted, google for nLite if interested.

  3. Jack says:

    I used the exe file as an admisistrator but it immedietly closed

    • Roy says:

      @Jack – well spotted, thanks for telling us. You’re right you can’t run sfc directly from within windows 7 as it just closes. You need to run it from an elevated command prompt instead.

      I have updated the article above with the correct procedure to run SFC in Vista and W7.