Some users have reported an issue in which iTunes stalls on the “One Moment Please connecting to the iTunes store” screen and never proceeds past that point.
It appears that, in most cases, this issue involves a problem with Parental Controls.
Fix
As discovered by Apple Discussions poster CommanderT, this problem can usually be solved via the following process.
In iTunes, navigate to Edit -> Preferences -> Parental Controls, then check the box next iTunes Store, and allow access to iTunes U. Click OK. Attempt to access the iTunes store. If it works, you can go back to Preferences uncheck iTunes Store.