How to Repair Corrupt or Damaged Windows System Files with System File Checker

Sometimes one of the important Windows system files can get corrupted. Then you may get messages about missing DLL files or have other indications that there is a problem. This tip will discuss repairing the system with System File Checker (SFC).

This is one of the numerous  command-line system tools that come on all current versions of Windows. It will scan all protected system files and replace incorrect or damaged versions with copies from a backup cache or from an installation disk or folder.

Malware infections are one source of this type of problem so make sure your system is clean before trying repairs. Also, System Restore is easier to use and should be tried first if possible.

Using System File Checker in Windows XP

1.    Open a command prompt (or the Start-Run line).
2.    Type and enter "sfc /scannow" (without quotes but with the space).

Your files will then be scanned and repaired if necessary. It may take 10 or 20 minutes, depending on your system.

Unfortunately, in Windows XP it is quite possible that SFC will first ask for your Windows installation disk. Most people only have a restore disk so it is necessary to take some rather involved steps before running SFC. Even if you have an installation disk, it probably won’t work unless Service Pack 3 is on it. A discussion of how to proceed if you have no proper installation disk is at this Bleeping Computer forum.  

Using System File Checker in Windows Vista/7 

The procedure generally goes much smoother in the newer versions of Windows. 

1.  Open a command prompt with administrator privileges.
2.  Type and enter "sfc /scannow" (without quotes but with the space). 

Your files will then be scanned and repaired if necessary. Again, it may take 10 or 20 minutes, depending on your system. 

If your Windows Vista/7 system won’t boot, there is still a possible way to try a repair. In such cases, SFC can be run offline using  the Windows Recovery Environment (RE). Again, the catch is that you need a setup disk. Details of using RE can be found at WinHelpOnline.

After running System File Checker

It is best to go to Windows Update after any repair is done to ensure that you have the latest file versions.

As an aside, my personal preference for dealing with corrupt files is regular backups. However, when helping other people (who didn't back up) SFC has its place and is part of the regular toolkit.   

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This tips section is maintained by Vic Laurie. Vic runs a Windows blog called The PC Informant and also operates a computer education website.

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by babagay on 14. December 2013 - 5:57  (112935)

has 25gb pysics,science,maths books.suddenly windows help system not working,networking not working,dsl stopped working.means windows got corrupted.restore points were deleted before this coz they werent working properly.sfc/scannow not working asking for windows xp sp 3 cd and when i put it in cd drive then a message comes to put cd in drive and this message comes repeatedly after some time.
if there is a virus its solution is antivirus.
if there is windows corrupted then whats solutiion.i mean there should be a more punishing name for windows xp corrupted.
there should be more than one soluition for windows corrupted not one or two solutions.

by MidnightCowboy on 14. December 2013 - 6:17  (112936)

We are unable to respond to support requests in the comments sections. Please post details of your issue here in our forum. MC - Site Manager.

by uros on 27. August 2013 - 12:44  (110348)

I have a problem whent a started an pc it shoved to press start windows normaly, safemode,safe mode with command prompt,last known good configuration and when i pressed evry one of them it showed up .Windows failed to start. A recent hardware or software change,might be the cause and this

Windows failed to load because a critical syset driver is missing or corupt and a bunch of other things and some status:oxcoooooof and after i press enter
choose an operating system to start.,or press
TAB to to select a tool then there is windows 7 to press and to press tab for windows memory Diagnostic and when i press enter again on wondows 7 it is back on the first page please help

by v.laurie on 27. August 2013 - 12:58  (110353)

Unfortunately, we cannot answer individual support questions like this in the comments. Please post your question in the forum:

by LeocXD on 28. April 2013 - 16:57  (107368)

I have a problem where it will go to a certain percentage, then it'll say "Windows Resource Protection could not perform the requested operation". I've tried doing "sfc /scannow" over and over again but it won't work. What do I do?

by v.laurie on 28. April 2013 - 17:18  (107369)

Unfortunately, SFC fails for many reasons. This type of question is beyond what can be answered here. Please log in to the Freeware Forum and post your questions in General Computer Support. Please provide more information about your system when you post there. Knowledgeable people there will gladly try to help you.

by DreAgeN (not verified) on 15. October 2012 - 13:24  (100781)

My files says "cannot read from the source files or disk" . Ahhhh! How to repair it

by TheSomeDude (not verified) on 25. August 2012 - 7:32  (98282) if you whana enable it again.

by crome221 (not verified) on 16. August 2012 - 19:35  (97820)

I did what you said, but it said "Windows Resource Protection found corrupt files but was unable to fix some of them.
Details are included in the CBS.Log windir\Logs\CBS\CBS.log. For example C:\Windows\Logs\CBS\CBS.log

i have a vista computer. yes i ran as administrator will doing this.

i'm looking for information because my computer said that my ANTI Virus software CA security has 1-3 corrupted and unreadable files. and says to run Chkdsk utility which i did i went to CMD ran as admin, i put in (without quotes)"chkdsk /f" told me to "the type of the file system is NTFS. Cannot lock current drive.
Chkdsk cannot run because the volume is in use by another process. Would you like to schedule this volume to be checked the next time the system restarts? "
i put in Y and press enter.
and it says "This volume will be checked the next time the system restarts."
so i restarted and nothing happened because the corrupted file was still there.

so i tried system restore which is in the Accessories/System Tools but this happened on tuesday and it won't restore to monday it only restores to wensday.

please help me i just want to take care of this already.

by v.laurie on 16. August 2012 - 19:45  (97822)

This type of question is beyond what can be answered here. Please log in to the Freeware Forum and post your questions in General Computer Support. Knowledgeable people there will gladly try to help you.

by crome221 (not verified) on 16. August 2012 - 19:40  (97821)

and can you tell me of to find the Details that are included in the CBS.Log windir\Logs\CBS\CBS.log ?

by varnagal (not verified) on 23. July 2012 - 22:30  (96557)

I would like to install the system checker as the computer got a virus and corrupted many files. I would also like to review the comments made about this product. Thanks for offering this free!

by JasonM (not verified) on 14. April 2012 - 22:10  (92102)

One of the best tips I can give for those having issues with to simply turn off your UAC. See the only thing it is, is an hinderance and it causes more problems than you know.

If you have up to date internet security, then quite why you'd want to run this thing is beyond me.

The vast majority of people using windows 7 are using the 64 bit version of which ever install they use.

There is zero security issue...the UAC is there for stupid inform them they are about to install software...that's it!

turn of UAC, then run sfc /scannow and you will be sorted..without any problems...the uac is the main cause of sfc not being able to repair.

by wj.ccsi (not verified) on 24. June 2012 - 14:16  (95310)

You obviously know very little about what exactly UAC does.
It is not recommended to shut it off. Shutting down UAC simply reverts WIndows 7 back to the XP security model. Bad idea all around.

by MidnightCowboy on 15. April 2012 - 5:39  (92117)

Windows 7 x32 bit users still make up 15% of operating systems which is quite a lot. Gizmo's Freeware does not recommend to disable UAC at all. Microsoft built this code and it's prompts for good reason and it should be left alone.

by ebeidy on 29. March 2012 - 5:41  (91362)

I tried this method, it is gone very somoothly,BUT unfortunateky my free avast antivirus crashed. I dont know why??

by Momscriber (not verified) on 2. February 2012 - 4:06  (88159)

I have the same issue - sfc /scannow on vista said it found corrupted files that it could not fix and that I could see details in cbs.log. However, when I try to look at cbs.log, it says "access denied". I have administrator access and ran sfc /scannow as administrator, and I tried accessing cbs.log using administrator command prompt but still got "access denied" message. Is this important enough to need to figure out and fix? How else can I find out which files are corrupted?

by MidnightCowboy on 2. February 2012 - 5:44  (88161)

Sorry but we are unable to provide individual support here in the comments. Please post your question in our forum.

by morrig on 26. August 2011 - 10:06  (78381)

AN excellent tool that's simple to use and does all round repair of a Windows system-

by Angelspawn666 (not verified) on 13. April 2011 - 13:40  (70099)

I've also had the same problem for 6 months now sfc /scan now is easy.. but no were no knowledge does it say how to fix the dam errors.. you think people would say and not have to do a factory default re-install os which doesn't cure it either. its just plain stupid really... sick and tired of reading forum after forum .. they need to make a program that directly fixes the issues and such little cost or some proper FAQ's because it not getting anyone anywhere

by Adrastos (not verified) on 10. October 2010 - 1:34  (59334)

I too have tried this and find that there is a corruption that it can't fix. I got this after it Verified my system. Windows Resource Protection found corrupt files but was unable to fix some of them Details are included in the CBS.log windir\logs\CBS\CBS.log.

I ran with admin rights and it wouldn't let me pull up the log file. System seems to work just fine. Not sure what could be corrupt. Did a fresh install less than a month ago.

by MidnightCowboy on 10. October 2010 - 8:00  (59343)

I had this same issue with Windows 7 x32 after using a program called AppRemover to uninstall AVG9. I reported the flaw to the developers who quickly released an updated version but unfortunately this didn't help me.
From what I could tell, a new install of Windows was going to be the only way forward although I've since taken the easy way out and moved to Linux :)

Despite my comment above I highly recommend AppRemover as being the best specialist tool for removing security programs. Using the system uninstaller can leave remnants behind which will conflict with installations of new software, and using a third party uninstaller with more aggressive settings like Revo can remove shared components which other programs need to function.

by Roberteh (not verified) on 8. October 2010 - 22:42  (59276)

Any amount of updates/sp's over & above the first installation from the OS disc makes this effort "sfc /scannow" fruitless as Windows(XP)clearly states, the current operating system is newer than the one wanting to access/install from & I can't go any further.

by v.laurie on 8. October 2010 - 23:16  (59279)

As I say in the tip, you need a disk with the SP3 version. You might get some help from the reference Pilgrim mentions (

by Pilgrim on 8. October 2010 - 10:29  (59190)

XP users might find this of use:

by Lynn houston (not verified) on 7. October 2010 - 2:58  (59134)

Ran sfc /scannow on vista. It said it found corrupted files that it could not fix and that I could see details in cbs.log. However, when I try to look at cbs.log, it says "access denied". I tried changing permission rules, but nothing. How can I look at the file and any idea how I can fix the corrupted files once I find out what they are? Thanks

by Lynn houston (not verified) on 7. October 2010 - 5:12  (59137)

finally got access to cbs.log, but it's greek to me. Seems some files were corrupted and they were unable to be repaired. Short of reinstalling windows, how can I fix the files?

by v.laurie on 7. October 2010 - 14:47  (59150)

As much as I would like to help, it is not possible for me to give detailed assistance with specific individual problems. Systems vary too much.

by v.laurie on 7. October 2010 - 3:33  (59135)
by willem (not verified) on 6. October 2010 - 17:04  (59119)

Laurie, I select the sfc.exe rightclicking and choosing to execute with administrator priviliges. That's the way?

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