Update: Another possible solution that I did not try is recommended by Yousuf Omar is the following: 1-sign out from the store menu 2-de authorize computer 3-sign in again and every thing is up and running. If it works then please tell us.
I had a strange problem in iTunes in the last 2 weeks. Suddenly the iTunes Store section in the app is stuck with “One Moment Please” on the screen. You can’t enter the store or view your account. I did not find the cause of this problem but I know of one solution to fix it.
Important Notice: the fix will reset your iTunes settings. It will not delete your applications/playlists/library etc. Go go to iTunes menu then Preferences and take a note of your settings.
Now quit iTunes then using Finder go to your home folder ( /Users/yourname ) then go to Library then Preferences folders ( /Users/khaled/Library/Preferences for example).
Locate the file named com.apple.iTunes.plist then move it to your desktop folder. Restart or just start iTunes again. iTunes will generate a new com.apple.iTunes.plist file.
Check if iTunes Store is working or not.
This is the method I have used. Tell if you had the same problem, know a better fix or even know the cause. All comments are appreciated.
Arabic version of this post on SaudiMac.net.