How to Fix or Reinstall Windows Installer
- 1). Navigate to the Windows Installer download page (see Resources).
- 2). Click the "Download" button corresponding to your version of Windows and save the file to your hard drive. If you're unsure which version is meant for your operating system read the reference provided under "Instructions" on the download page.
- 3). Double-click the downloaded file to start the automatic updater. Follow the onscreen instructions to complete the installation process.
Source...