Freeze in loading Mojang

Why, when I want to play Minecraft in loading Mojang, the loading freezes and I can not do anything, I can not change pages, I can not close the page of Minecraft and the only solution is to turn off my computer, then turn it back on, but I still can not play because it will do the same for me.

So I would like to know if you have any idea of how to solve the problem?

thank you in advance