I JUST UPDATED TO EL CAPTIAN AND NOW IT JUST MAKES A SOUND AND HAS BLACK SCEEN WHEN STARTS UP
MacBook Pro with Retina display, OS X El Capitan (10.11)
visit this site, it should help
http://appletoolbox.com/2015/10/mac-os-x-el-capitan-will-not-start-up-after-upda te-fix/
Hi! Maybe this Apple Support article will help you:
About the screens you see when your Mac starts up - Apple Support
Have you tried a SMC reset?
https://support.apple.com/en-us/HT201295
Depending upon the model/year MBP that you have, the problem may be covered here:
https://www.apple.com/support/macbookpro-videoissues/https://www.apple.com/support/macbookpro-videoissues/
Ciao.
MACBOOK PRO 2014 FREEZES AFTER OS UPDATE
