Screen turns black and mouse won't click
When ever I'm working on my computer all of a sudden the screen turns black and the mouse won't click almost like it locks up. It usually last about 30 seconds long and it will go right back to where I'm working when I'm done. I was just wondering what i was doing wrong and what i need to change.
thanks in advance
MacBook Pro with Retina display, iOS 9.0.2