MacBook Pro failure to start up after update.

I updatd to the new apple software to my MacBook Pro and on its restart it loads to the point that it shows the apple symbol with a progress bar and then shuts down before I can get to the home screen. Have attempted a restart on 3 or 4 occasion with no success.

I have also attempted a genius bar appointment with no success due to no availability of appointments.

Any help would be appreciated?