try this courtest of Mick Murphy
Removing and reinstalling iTunes, QuickTime, and other software components for Windows Vista or Windows 7
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Or, use the Program below to uninstall iTunes, if you have a prior and corrupted version installed..
Once you do that, re-download/save iTunes to the Desktop > right-click on its setup.exe > Run as Admin
http://www.revouninstaller.com/revo_uninstaller_free_download.html
“Revo Uninstaller helps you to uninstall software and remove unwanted programs installed on your computer even if you have problems uninstalling and cannot uninstall them from "Windows Add or Remove Programs" control panel applet.
Revo Uninstaller is a much faster and more powerful alternative to "Windows Add or Remove Programs" applet!
With its advanced and fast algorithm, Revo Uninstaller analyzes an application's data before uninstall and scans after you uninstall an application. After the program's regular uninstaller runs, you can remove additional unnecessary files, folders and registry keys that are usually left”
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Any further iTunes problems, contact Apple for Support with their Software:
http://www.apple.com/support/itunes/