Why does the screen keep freezing? It won't let me do anything! Help!

I have a Lenovo N22 chromebook, it won't power down, none of the keys do anything and the screen is frozen, it did this a long time ago and I waited for it to fix, it took a week and a half for it to fix itself, and I don't want this time to be longer. Even when I close it, it’s still on! Someone have this same problem?