There are many reasons why windows updates may fail to install, either when using automatic updates or the Microsoft web tool. Below are listed some of the more common fixes.
FIX 1
1. Stop the automatic updates service(if running) using
net stop wuauserv
2. Delete the contents of the DataStore folder in %windir%\SoftwareDistribution.
3. Start the automatic updates service using
net start wuauserv