Tech Tips: Windows Update failing? Try this

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http://support.microsoft.com/kb/947821

Windows corruption errors prevent Windows updates and service packs from installing. For example, an update might not install if a system file is damaged. If the error you see is in the following list, try the solution in this article.

0x80070002 | 0x8007000D | 0x800F081F | 0x80073712 | 0x800736CC | 0x800705B9 | 0x80070246 | 0x8007370D | 0x8007370B | 0x8007370A | 0x80070057 | 0x800B0100 | 0x80092003 | 0x800B0101 | 0x8007371B | 0x80070490

If your error is not listed or if you are running Windows XP, try Solutions for common Windows Update errors.

Resolution

Windows 8.1, Windows 8, Windows Server 2012 R2 or Windows Server 2012

To resolve this problem, use the inbox Deployment Image Servicing and Management (DISM) tool. Then, install the Windows update or service pack again.

1. Open an elevated command prompt. To do this, swipe in from the right edge of the screen, and then tap Search. Or, if you are using a mouse, point to the lower-right corner of the screen, and then click Search. Type Command Prompt in theSearch box, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.
2. Type the following command, and then press Enter.
   It may take several minutes for the command operation to be completed.
   DISM.exe /Online /Cleanup-image /Restorehealth
   Important When you run this command, DISM uses Windows Update to provide the files that are required to fix corruptions. However, if your Windows Update client is already broken, use a running Windows installation as the repair source, or use a Windows side-by-side folder from a network share or from a removable media, such as the Windows DVD, as the source of the files. To do this, run the following command instead:
   DISM.exe /Online /Cleanup-Image /RestoreHealth /Source:C:\RepairSource\Windows /LimitAccess
   Note Replace the C:\RepairSource\Windows placeholder with the location of your repair source. For more information about using the DISM tool to repair Windows, reference Repair a Windows Image.
3. Close the command prompt, and then run Windows Update again.

DISM creates a log file (%windir%/Logs/CBS/CBS.log) that captures any issues that the tool found or fixed. %windir% is the folder in which Windows is installed. For example, the %windir% folder is C:\Windows.

Windows 7, Windows Vista, Windows Server 2008 R2 or Windows Server 2008

To resolve this problem, use the System Update Readiness tool. Then, install the Windows update or service pack again.

1. Download the System Update Readiness tool.
   Click the download link in the following table that corresponds to the version of Windows that is running on your computer.
   Find out if your computer is running the 32 or 64-bit version of Windows
   
   This tool is updated regularly, we recommend that you always download the latest version.