this morning I updated my Late 2011 15" MBP in to 10.11.5. I couldn't get the upgrade to work from the App Store, so I downloaded the "combo" upgrade from a link someone posted here. The computer work for a while, but then when I was using Sketchup, it clicked and I got a blue screen. It was frozen, and I held down the off button to shut it down. I powered it up again, and the start-up as slow, and then went to a blank white page. I powered it off again, and tried starting it in safe mode. Still a white screen. I powered it off again, and now when I tried to start it up, I got the apple and the bar started, but the bar stopped about 3/4 and it's been stuck there for about 10 minutes so far. Help. Please.