I googled it and found this:
SFC /SCANNOW-WINDOWS FILE PROTECTION
Windows XP has the ability to protect itself from system instability caused by the overwriting important system files. This is a problem with Windows 95 and Windows 98. With the introduction of Windows Millennium Edition, Microsoft made a strong effort to stop this from happening. Now, in Windows XP, there is a much better protection of these important files. This system is called Windows File Protection
Windows File Protection is always enabled and allows Windows digitally signed files to replace existing files safely. If you introduce a file replacement in any other way, Windows File protection will overwrite your file!
An important part of Windows File Protection is the command line utility: System File Checker (sfc.exe) This is a great tool for troubleshooting Windows XP problems.
USING SFC /SCANNOW
The main reason for using this utility is when you suspect there may be a problem with a Windows XP system file. Perhaps you get a dialog box appear informing you of a problem with a .dll file, or your program will just not load! It is therefore worth checking to see if there are any corrupt system files using scannow sfc.
To do this simply go to the Run box on the Start Menu and type in: sfc /scannow
This command will immediately initiate the Windows File Protection service to scan all protected files and make sure of their correctness, replacing any files that it finds with a problem.
A bos should appear to give an indication of how long the process is taking.
If all goes as it should, any corrupt, missing or incorrect files would be replaced by this process. However, as with most actions in this world, things can go wrong and the following should help!
The most frequent complaint with scannow /sfc is that a dialog box appears asking you to insert your Windows XP CD-ROM to continue.
Why does this happen?
There are several settings in your computer's registry that are checked when you run scannow /sfc.
As stated before, the Windows File Protection constantly monitors for any changes to the main system files. These are usually stored in:C:WINDOWSSystem32Dllcache (C: in most cases is the root drive)
The dllcache folder is extremely important so Windows XP hides it from you! To view it go to:
My Computer -> Tools -> Folder Options -> View -> "uncheck" Hide protected operating system files.
There is normally no need for the original XP CD to be inserted as your computer has a copy it can get hold of in this cache.
But, if the Dllcache folder, or part of it, has become corrupted for some reason then you will be prompted for the XP CD - so your computer can get a clean copy!
However, not ALL installations of Windows XP have ALL the system files cached into this folder! You may only have around 25-50MB of files in this folder under Windows XP depending on the settings in the registry.
HOW TO WORK AROUND THIS
As well as having a cache of all the system files on your PC, you should have the I386 folder from the XP CD installed on your hard drive. After doing this, it is quite simple to modify the registry to tell it the source path for these files.
This prevents 99% of requests for the the XP CD with Windows File Protection and the I386 folder also contains many other files that are sometimes needed by the operating system and this stops those requests for the XP CD,as well.
HOW TO PUT I386 ON YOUR ROOT DRIVE:
You will need to get your XP CD and locate the folder called: I386
This is a major folder and should be one of the first you see, now copy this onto your hard drive into the system root. For most of you that is going to be C: so you should end up with a folder that looks like: C:I386
Your computer needs to know that you now have the necessary files on your PC. This is done by editing the registry. Here's how: (type regedit in the Run box on the start menu)
By navigating to:HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionSetup
You will see various entries here on the right hand side.
The one we want is called: SourcePath
It probably has an entry pointing to your CD-ROM drive,(usually D:) and that is why it is asking for the XP CD. All we need to do is change it to: C: Now, double click the SourcePatch setting and a new box will pop up allowing you to make the change to the drive letter of your root drive, probably C:
Now restart your computer and try sfc /scannow again! (Courtesy of: compphix.com)
Please tell me if this fixes it!
Edited by AgentMES, 19 January 2008 - 02:39 PM.