The System File Checker tool, "scans all protected system files"
and compares them against a cache of the original file.
If a corrupt file is found, it is over-written with the cached version.
reference ...<(MS System File Checker)
Corrupt system files can be caused by several things, including viruses.
I always run SFC after a new install of Windows to insure a proper installation.
It's necessary to be running as an Administrator and have the OS Disc in the CD\DVD drive.
If you don't have an OS Disc, SFC may read the needed files from a recovery partition.
The System File Checker can be invoked by (clicking) the Start Button >>>
Run >>> type-in the following command, "sfc /scannow" >>> OK.
The System File Checker tool is, also, accessible from Command Prompt.
(click) the Start Button >>> All Programs >>> Accessories >>> Command Prompt.
Type-in the following command, "sfc /?", this will show all available
switches and a description for each one.
This is how I make a shortcut to the System File Checker.
I find it useful to keep on a thumb-drive and move from machine to machine.
Mostly, It comes in handy if you don't want to remember the command. :)
To make the shortcut, (right-click) an empty area on the desktop >>>
New >>> Shortcut >>> type-in the following command,
"%windir%\system32\sfc.exe /scannow" >>>
Next >>> Name the Shortcut >>> Finish. To change the icon,
(right-click) Shortcut >>> Properties >>> Change Icon >>>
type in the following command, "%SystemRoot%\system32\shell32.dll"
and press "Enter" >>> Select an Icon >>> OK all the way back to the desktop.