Uninstall iTunes in Windows is rather difficult. Before reinstall you should uninstall first. I found this for you in an older thread (read carefully):
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Note that the following procedure involves a registry edit. Back up your registry prior to proceeding.
(1) Do a complete uninstall of iTunes and related software components as per the instructions in the following document (but do not attempt to reinstall iTunes just yet):
Removing and reinstalling iTunes, QuickTime, and other software components for Windows Vista or Windows 7:
http://support.apple.com/kb/HT1923
(2) Launch Regedit as an administrator. In your Start Search field, type regedit. Right-click on the Regedit entry that comes up and select "Run as administrator" as per the following screenshot:
(3) In the left-hand pane of Regedit, click the triangle next to HKEY_LOCAL_MACHINE to expand its contents.
(4) Expand the contents of SOFTWARE
(5) Expand the contents of Microsoft
(6) Expand the contents of Windows
(7) Expand the contents of CurrentVersion
(8) Expand the contents of Installer
(9) Expand the contents of UserData
(10) Expand the contents of S-1-5-18
(11) Right-click on Components and select "Permissions" as per the following screenshot:
(12) In the "Permissions for Components" screen that comes up, click the Advanced button:
(13) In the "Advanced Security Settings for Components" screen that comes up, click the "Owner" tab.
(14) In the "Owner" tab, check the "Replace owner on subcontainers and objects tickbox, select "Administrators" and click Apply:
(14a) If (after clicking Apply) you receive a "Registry Editor could not set owner on the key currently selected, or some of its subkeys" message, click OK:
(15) Click OK in the "Advanced Security Settings for Components" screen.
(16) Click OK in the "Permissions for Components" screen.
(17) Quit out of Regedit.
(18) Try installing iTunes using the latest version of the iTunes installer downloaded from the Apple website:
http://www.apple.com/itunes/download/
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