System File Checker

This is handy tool I found. Have you had a Windows system encounter problems due to corrupted system DLLs? A while back I encountered that on a Win7 system that would refuse to run Windows Updates with a "Program cannot start because sqmapi.dll is missing" error. It wouldn't run an offline SP1 install either due to the same problem.

The solution: System File Checker.

Steps:

1. Open an elevated command prompt (Start -> type "cmd" -> Right-click the cmd shortcut and select "Run as Administrator"
2. Provide admin credentials if UAC prompts you.
3. Type: SFC /scannow and press enter. The program will take a few minutes to check each system dll for corruption and for wrong versions, and replace them as needed.
4. When it's finished, type findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log >%userprofile%\Desktop\sfcdetails.txt to put a log file onto your desktop, which you can review to see what was updated.
5. Repeat steps 3-4 two more times (run SFC three times) to ensure that no files were missed. You may want to reboot after each run - though when I did it I didn't have to.
6. Profit! (ie I was once again able to run Windows Update normally and get the Service Pack installed)

I've only used this on Windows 7 (Enterprise), but it's a feature that was introduced with Vista.

Microsoft support link:
http://support.microsoft.com/kb/929833