My entire website is pretty much dead after 4.2.3

Hi,

Could you elaborate a little on this, what is it that isn’t working for you?

Some shortcodes may not work after the security release, this is when shortcodes have been used in the incorrect manner, and a update to the plugin/theme that created the code, or changing the format of it in your post should resolve this but I’m going to need ab it more information to go on to be able to point you in the right direction here ??