How do you unlock the store?
You can't. Lingots are in beta currently, so only (randomly chosen) beta testers have them. But maybe this week: http://www.duolingo.com/comment/805193
I must be one of these beta testers, and I can still view the store, but I can't buy anything. The buttons don't work. It used to work. If you disabled it temporarily, you don't need to reply.