can't shut it down or reboot my ubuntu 15.04

I have my asus x551ma, I installed Ubuntu 15,04 and it was working good but, now I can't shut it down or reboot or even logging out from the угол above. It only works when I использовал терминал by typing:

sudo  shutdown -p now 

but not the other нормальный way. Please is there anybody that хан help я?