Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple Suffering iTunes Store Outage Worldwide
We have had multiple reports from around the world that the iTunes store is currently down around the world. We were still able to access the store from all of our iOS devices but not from either a Windows machine or a Mac.
This outage follows several previous outages to to the iTunes store in recent months.
Update: The iTunes store is slowly coming back online