Macbook won't let me sign in to icloud

I need help. My macbook won't let me sign in to icloud, i've tried everything, i've restarted and shut down the macbook and i've made sure there are no updates and everything.

what happens is i type in my apple id in the icloud section of the system preferences, it buffers, i type in my password (it's the correct password), it buffers at the apple id section, then the password section disappears and goes back to the apple id section....like what is happening?!!!!!!!!!

if anyone can help me it would be much appreciated.