I had someone with this issue once. To fix it we deauthorized itunes from the computer. Then we used revo uninstaller to uninstall everything associated with itunes and re-installed. It fixed the problem in this case.
Use Windows add/remove to remove iTunes instead:
uninstall iTunes and related software components in the following order. Then, restart your computer. Do not restart until all are removed - even if it prompts
Apple Software Update
Apple Mobile Device Support
Apple Application Support (iTunes 9 or later)
After following the previous steps, you should confirm that the following files and folders have been removed and if any are left behind, remove them now:
C:\Program Files\Common Files\Apple\
C:\Program Files\iPod\ Note: Follow the additional steps at the end of this article if you receive the alert "Cannot delete iPodService.exe: It is being used by another person or program" when trying to delete this folder.
Follow these steps if the message, "Cannot delete iPodService.exe: It is being used by another person or program" appears when you try to delete the iPod folder.
Make sure that iTunes and the iPod Updater utility are not open.
Press and hold Control-Alt-Delete. Select Start Task Manager.
Click the Processes tab.
Locate "iPodService.exe" in the list.
Click "iPodService.exe" and choose End Process.
Quit the Task Manager.
Reboot machine and run CCleaner - to ensure you clean the registry
Reinstall the latest version of iTunes: http://www.apple.com/itunes/download/