Part of being able to successfully
troubleshoot the Windows operating system is being able to
troubleshoot the applications that are installed on the operating
system. At least half of all troubleshooting calls will be concerned
with troubleshooting applications.
Windows Application Missing/Corrupt .DLL or .VXD Files
Two important types of files that are associated with the operating
system and its applications are .DLL and .VxD files. As previously
discussed, what these files do and how to repair them is critical to
the health of the system. If they get deleted or become corrupt, the
system applications will no longer run properly and the system may not
be able to start up properly or start up at all. Another important set
of files called the Dynamic-Link Library (.DLL) files were also
previously mentioned. These small files store subroutines that either
come with the application, or are made by the programmer. The loss or
corruption of .DLL files will cause an application to lock up or
prevent it from loading. Problems arise when a new application is
installed and then updates the shared .DLLs, creating a .DLL conflict.
As a result of this conflict, older applications may not be able to
handle the updated file and will fail to work.
SFC Utility
The System File Checker (SFC) has also been discussed earlier in this
chapter. The command-line utility can be used to scan the operating
system files to ensure that they are the correct (original Microsoft)
ones. Although it is not as widespread a problem as it was in the past
(with Windows 3.x, for instance), it is possible for some applications
to replace system files (for instance, .VxD or .DLL files) with
different files of the same name. The result is an operating system
that is no longer stable and has difficulty even booting after
installing or uninstalling some applications or utilities.
SFC is a tool that allows users to scan their system and verify
that versions of the protected system files are up to date. If a
protected system file has moved or has disappeared, SFC
automatically replaces the file with the correct version from the
.DLL cache folder, as earlier mentioned. Most of the time when the
SFC utility is run and the copy in the system folder is replaced,
the problem will go away. Unfortunately, many programs load their
own copy in their own folder, thereby causing the problem.
