Chosen Solution
Does not reboot after screen froze, pressing the keys CMD +R on start. Aparently downloads the program and instals it, but stays on the “black bar” for ages to no avail.
At this point I think you’ll need to pull the power cord wait a good 10 minutes and plug it in again and then try starting up the system. How far did it go this time? If you didn’t get back to your desktop, you’ll need to restart the system again this time pressing on the Shift key to get into Safe Mode. Reference: Use safe mode to isolate issues with your Mac If that failed let us know.
