try with this one
uninstall all the apple application S/w like Quicktime, Bonjour,
apple Device Support, Apple Auto update, Itunes etc from your pc,
Reboot it
Now download a fresh itunes from apple and try installing
Reboot it
If you are having Problem in uninstalling any of the apple application
try 'revo uninstaller' and uninstall all the apple applications
mentioned above