Okay, we first need to back up the files related to your iTunes library. Don't do anything else before you have these files secured.
Some data related to your iTunes profile is located in the following folder:
C:\Users\USERNAME\AppData\Roaming\Apple Computer\MobileSync\Backup
If you have trouble accessing the AppData folder (it doesn't show up, for example), you'll need to fix a few things. In the
C:\Users\USERNAME folder, look to the menu items at the top of the window. These are things like "File", "Edit", and "Tools". Under "Tools" select "Folder Options". Click the "View" tab in this window. You'll see a number of checkboxes. Make certain that "Hidden files and folders" has "Show hidden files and folders"
selected. Make certain that "Hide protected operating system files (Recommended)" is
unchecked. Click okay, and you should see the AppData folder.
Copy the
Backup folder to a safe location. On your desktop is fine.
Now, we need to backup your library. Depending on how large your library is, you may not be able to copy it; you might have to move it wholesale. Find the following folder:
C:\Users\USERNAME\Music\iTunes. If you have a "Music" entry in the upper right of your start menu, that should take you to where it is.
If you can copy your library, do so, copying it to a safe place. If you cannot, or you want to be lazy, rename the "iTunes" folder.
Now, you're all backed up. It's time to uninstall stuff. I'm going to refer you to a page on Apple's site:
Removing and reinstalling iTunes, QuickTime, and other software components for Windows Vista or Windows 7. Follow the instructions on that page, particularly with respect to the order you uninstall things. To see instructions for a particular product, like "Removing iTunes", click on the "Removing iTunes" item and it will expand.
Let me know if that does work. If not, we try something very similar, but more intrusive.