MacBook Pro error while trying to update

Hi all,

I tried to update my MacBook and after the loading screen, this came up along with a message that said there had been an error during the process. It is telling me to “select the system you want to use to start up your computer”, but nothing is loading for me to choose. I don’t have another computer or cable to use for target disk mode. This is been going on for hours and I’m not sure what else to do, whenever try to restart or shutdown the computer the same thing just happens. Any tips? Thanks in advance.