Hey Everyone! I had this same problem...worked for HOURS trying to solve. FINALLY found a solution. I provided a link for where you can fidn free where for both downloads you'll need. Remember to install the add on after you install QT Alternative. Both can be found on the link I provided.
1. uninstall QuickTime
2. Install Quicktime Alternative (
http://codecpackguide.com/quicktimealt.htm)
3. Install the QT alternative itunes add on
As soon as i did this...I was able to get into my itunes again after hours and hours of messing with it and trying everything else. there is really not much info about solving this problem...guess I got lucky.
Good luck!!