Thank you for your help.
I do not have another Mac at home.
But this solution with full recovery of Yosemite can install something to help. The model of my Mac is "MacBook Pro (Retina, 13-inch, Mid 2014)" and should possess this system restore functions. I fear me to something not worsened in the system. I do not have too much experience on Mac. What do you think about this solution with the "full system recovery"?
All my works correctly
I just have a problem with this application App Store.
Are you a computer scientist ?
Maybe you will send me a report which displays the App Store ?