Windows XP works very hard to maintain the integrity of the system files on your machine. If you try to replace one of the "protected" files, you may get an informative message that the operating system has put the old, approved, version back. Not all files are under system file protection, and even for those that are, there are ways around it. Occasionally system files become corrupt.

Enter the SFC, the System File Checker.

SFC is a good utility to run when you suspect that system files have been somehow corrupted. It validates the digital signatures of all of the Windows system files, and restores any that it finds are incorrect. It will use the on-disk cache, if possible, but SFC may require that you provide your original installation CD or a location with an image thereof. (See this prior article about not having an installation CD on some of the alternatives if that's the case.)

To run the system file checker, press Start, Run, and then type in SFC followed by its options.

The most common usage of SFC is this: SFC /scannow

This causes SFC to scan your system immediately. SFC can take a few minutes to run. As I said above, have your installation CD or equivalent available in case SFC needs to replace a damaged file.

While it's not documented anywhere, if SFC replaces any system files, I'd reboot. I just like to make absolutely certain that the file replacement actually takes effect.

The Microsoft knowledgebase includes more detailed SFC documentation including more options to check at boot time, control the size of the system file protection cache and so on. Speaking of which, the knowledgebase also includes System File Protection documentation, covering the mechanism Windows XP uses to keep your system files safe automatically.

Source: http://ask-leo.com Article 154 Posted February 28, 2004