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The System File Checker (sfc.exe) is an useful tool that lets you scan the integrity of Windows system files, and repair corrupt or missing system files. Numerous cases have been resolved thus far by running Sfc.exe with the "scannow" parameter. However, there are situations where in a corrupt or missing system file prevents Windows from booting normally, and running Sfc.exe from Windows isn’t possible. In such cases, Sfc.exe can be run offline using two additional parameters, via the Windows Recovery Environment (Windows RE) in Windows 7 and Windows Vista.
Booting into Windows RE
Configure the boot order in the BIOS such that the first boot device is your CD/DVD drive.
Insert the Windows 7/Vista Setup DVD and restart the computer.
Alternately, you may use the Windows 7/Vista System Repair Disc if you have one.
When prompted, press a key to boot from the DVD. In the "Install Windows" screen, clickRepair your computer
Select your Windows installation, and click Next
Editor’s Note: Make a note of the drive-letter of your Windows 7 installation, as seen from Windows RE. This is the drive-letter you want to reference when running Sfc.exe offline.
Click Command Prompt
To scan the integrity (and repair) a specific file, use this command:
sfc /scanfile=d:\windows\system32\zipfldr.dll /offbootdir=d:\ /offwindir=d:\windows
The above command scans the file zipfldr.dll and replaces it if required.
To scan the integrity of all system files and repair them, run this command:
sfc /scannow /offbootdir=d:\ /offwindir=d:\windows
This process takes some time (<5 min in my case) to complete, and there weren’t any integrity violations.
Source: http://www.winhelponline.com/blog/run-sfc-offline-windows-7-vista/
