iMac won't boot up after latest update

downloaded the newsest updates from Apple and now my computer won't start up. Goes to long in screen and won't let you type in pass word. Spinning Beach Ball of Death comes up and never stops.

I just keep shutting it down ( push off button on the back until it shuts off) and trying to start it again. Some times it will let you get a little farther, but always after 2-3 minutes it goes to SBBOD.

Lates thing I did was push option+command+S when I turned it back on and now screen is black and has a bunch of code. Been at this stage for 30 minutes now. It is not pluged into the internet at the moment.

Suggestions?