To fix this you have to go into C:/Users/Username/My Music/iTunes
You won't see the iTunes folder there unless you enable "Show hidden files, folders and drives", to do this go to 'Organize' -> 'Folder and search options' -> Click the 'View' tab -> Check 'Show hidden files, folders, and drives -> Click 'OK'
Your iTunes folder should now be visible in, go into it and you'll see 'iTunes Library.itl', delete that file then go into the 'Previous iTunes Libraries' folder and your last music library for iTunes 10.7 will be the one that is labled 'iTunes Library 2012-11-30.itl', the date is when you updated to iTunes 11, I'm going to assume it was today.
Copy the 'iTunes Library 2012-11-30.itl' file into the 'iTunes' folder and rename it to 'iTunes Library.itl'
If you haven't already, install iTunes 10.7 again and BOOM, you have the much better iTunes version back! 🙂