I just got off the tele with Apple support. This will not affect your library (database) of songs & videos. Here's what we did:
1. Go to the Apple in upper left corner and "Shut down" and restart the computer (Don't just "restart").
2. When booting completes, click on "Finder" then "Applications" and drag the Itunes app to the "Trash" on the desktop.
3. Empty the trash by righting clicking on the icon.
4. Click on "Finder" then "Downloads" and see if an iTunes installation package is in it. If so, also move it to "Trash" and "Empty Trash"
5. Go to the Apple in upper left corner and "Shut down" and restart the computer AFTER waiting 30 seconds (Don't just "restart").
6. When booting completes, start Safari and go to
www.apple.com/downloads
7. Click on the iTunes download button and COPY it to your desktop (or it may auto copy to your downloads folder, which is OK)
8. Click on the iTunes installer package and continue clicking until it says "Installation Successful" (or something to that effect......)
9. Go to the Apple in upper left corner and "Restart"
10. When booting completes, click on the iTunes icon and it should work (At least it did for me!............Good Luck