Why does my Acer Chromebook screen go black after I enter my password?

[msnkarla]

Sometimes it shuts off and won't turn on and other times the black screen stays on for 30sec-1 min before the main page comes on. I always use the onscreen button to shut if off when I am powering it down. It is only 6 mo old. I have had to return it once because the mic didn't work. Thanks.