How to Reinstall Windows Installerby Jeffrey Ober
The Windows Installer is an integral part of the Windows Operating System. If the installer has parts missing, the only place where you can find those parts to replace them is on the installation media (CD or DVD). Fortunately, Microsoft included a process whereby you can attempt to automatically repair all parts of the operating system that may be damaged, all at one time, and without you having to know what parts to fix. Just place your installation media in your computer and let it repair itself.
Place the Windows installation media in your computer (CD or DVD drive).
Restart your computer and boot from the CD/DVD. Some computers will do this automatically, some will ask you to "Press Any Key to Boot from CD."
After the Windows Installation screen appears, press the "Enter" key to continue the installation process. Be sure you do NOT press the "R" key on this screen for repair, we will do that on a later screen.
Press the "F8" key to agree with the Windows licensing agreement.
Press the "R" key now to start the repair process and attempt to repair the current Windows installation. The Windows system will then access all parts of the operating system, including the windows installer, and will attempt to repair anything that is missing or has been removed.