In recent days, many Xbox One users are reporting that the pinned apps an the store becomes unavailable in Xbox One with the message:
"Your store aren’t available. Sorry about that. They should be back soon." and
"Having trouble connecting. It might be a problem on our side. We’re working on it."
The solution is very simple. You need to have a hard-restart of Xbox One by pressing its power button by 10 seconds.
Related Forum Threads:
http://forums.xbox.com/xbox_forums/xbox_support/xbox_one_support/f/4274/p/1715697/4572616.aspx
http://forums.xbox.com/xbox_forums/xbox_support/xbox_one_support/f/4269/t/1712382.aspx
http://forums.xbox.com/xbox_forums/xbox_support/xbox_one_support/f/4267/t/1637783.aspx
http://forums.xbox.com/xbox_forums/xbox_support/xbox_one_support/f/4267/t/1711451.aspx
http://www.gamefaqs.com/boards/691088-xbox-one/68784374