How to Manually Reinstall & Fix Windows Update
Windows Update Agent is a program on your Windows operating system responsible for downloading and installing Windows updates directly from Microsoft's servers. If Update Agent gets damaged, a manual-install file is available from Microsoft to replace it. A few steps must be taken before it can be installed on a computer that already has an up-to-date version of Agent, as Windows will not install it if it detects the original installation.
Download the Windows Update Agent install package from the Microsoft website in one of two versions, the x86 or x64 (see Resources for links). If you are running 32-bit Windows, download the x86 version; 64-bit users should download the x64 version.
Open the Start menu.
Type "WindowsUpdateAgent20-ABC.exe /wuforce" in the Windows Search box, replacing "ABC" with either "x86" or "x64," depending on what version you downloaded. The "/wuforce" entry forces Windows to reinstall the Windows Update Agent regardless of the version currently installed.
Press "Enter" to start the installation process. Once the process is finished, the Windows Automatic Update Agent will be fully repaired and restored.