Hey there Jantje1,
It sounds like you are unable to launch iTunes and get an error message instead. I would try the troubleshooting outlined in this article named:
iTunes for Windows Vista, Windows 7, or Windows 8: Fix unexpected quits or launch issues
If it comes down to uninstalling, then re installing iTunes altogether, use this link to download the 64 bit version of iTunes directly.
iTunes 11.1.3 for Windows (64-bit)
Thank you for using Apple Support Communities.
Yep, the short of it is simply copying and pasting a file fixed the problem for me. I have the latest 64 bit version ofo iTunes and Windows 8.1. This worked. I just rebooted afterwards.
Copy QTMovieWin.dll from: C:\Program Files (x86)\Common Files\Apple\Apple Application Support
to: C:\Program Files (x86)\iTunes