Hi Kathleen,
Sometimes, this issue happens when the latest iTunes was not installed properly or was interrupted during the installation process. Don't worry, all you have to do as you are using a Windows computer is to uninstall iTunes and all its components. Meaning, not only iTunes but the quicktime player and others as well. Then install the latest version of iTunes. Your music will not be deleted since they are on your hard drive but it is still okay to have a backup of them, in that way double prevention is already done.
To uninstall completely iTunes (including its components), please read these articles:
iTunes 11.1.4 for Windows: Unable to install or open
http://support.apple.com/kb/TS5376
Removing and reinstalling iTunes, QuickTime, and other software components for Windows Vista or Windows 7
http://support.apple.com/kb/HT1923
Removing and reinstalling iTunes, QuickTime, and other software components for Windows XP
http://support.apple.com/kb/HT1925
Note: Titles you purchased from the iTunes Store or imported from CDs are saved in your iTunes folder by default and are not deleted by uninstalling iTunes. Backing up your iTunes library regularly is recommended.
After successfully uninstalling iTunes, please ensure you have upgraded to the latest Service Pack for Windows by installing all updates available to you on Microsoft Windows Update:
http://update.microsoft.com
Once you have the latest Service Pack for Windows installed, download and install iTunes for Windows:
http://www.apple.com/itunes/download
I trust all will be okay. Take care.