Downloaded the El Capitan update this morning and started the install. It did its restart thing and has hung with the progress bar stuck at about 75%. It has stayed in the same place for over 4 hours. Any ideas as to what could be wrong? This is on a late 2011 MBP with 16gb and a Samsung SSD with over 100gb free. Upgrade is from 10.11.3. My current internet connection is a little slow but I was able to download the upgrade in an hour or so.