My computer was unable to do error checking (chkdsk) and errors began to
accumulate. System restore did not go back far enough to restore this
function. System File Check identified a corrupt system file "autochk.exe"
that sfc was unable to repair. Instead of doing a clean install, I was able
to do an Upgrade Install that preserved my programs, devices, settings, etc.
(see John Barnett Windows MVP).

I wanted to replace my corrupt system file with a good one from the Vista
Install DVD without having to do a complete install, but was unable to do
this until now. From multiple sources including contributors on Vista
Communities, Windows IT Pro, How-To Geek, and Vistax64 Forum, I have put
together a tutorial on how to access files from your Vista Install DVD that
you can use to replace corrupt files in your OS. See the link below:

[url]http://www.vistax64.com/tutorials/86959-access-vista-install-dvd-files.html[/url]

System File Check will identify corrupt system files that it can't repair
(see CBS.log). You can replace your corrupt files with good copies from the
Vista Install DVD. Many thanks to those who contributed to this solution.